Colour and anthocyanin stability of red
J Sci Food Agric 1998, 78, 565È573
Colour and Anthocyanin Stability of Red
Raspberry Jam
Cristina Garc• a-Viguera,1* Pilar Zafrilla,1 Francisco Arte s,1 Fernando Romero,2
Pedro Abella n2 and Francisco A Toma s-Barbera n1
1 Dpto Ciencia y Tecnolog• a de Alimentos, CEBAS-CSIC, PO Box 4195, 30080, Murcia, Spain
2 Dpto de Calidad y Desarrollo, Hero Espan8 a, SA Alcantarilla, Spain
(Received 3 November 1997 ; revised version received 23 February 1998 ; accepted 6 April 1998)
Abstract : Anthocyanin and colour stability of red raspberry jams made from two
di†erent varieties (“ZevaÏ and “HeritageÏ) were analysed during 6 months, stored
at three temperatures (20, 30 and 37¡C). Also the inÑuence of freezing the fruit,
previously to jam manufacture, was evaluated. Di†erent anthocyanin composition was detected for both cultivars and while “ZevaÏ fruit had a higher total
anthocyanin content, Heritage variety produced jams with a higher redness hue.
The development of browning was directly related to storage temperature but
not to thawing or the variety of fruit used. ( 1998 Society of Chemical Industry.
J Sci Food Agric 78, 565È573 (1998)
Key words : raspberry ; jams ; anthocyanins ; cultivar ; colour ; storage ; stability
cyanin composition and stability, and to deÐne the
changes in colour and pigment composition which may
occur during processing and storage at di†erent temperatures for 6 months. The inÑuence of freezing the
fruit previously to jam manufacture was also examined
as pigment degradation may take place during thawing.
INTRODUCTION
Colour stability of red fruit or red fruit products is
inÑuenced by many factors which have been previously
reported (Markakis 1982). Temperature and time of
processing (Decareu et al 1956 ; Markakis 1982 ; Pilano
et al 1985) and storage (Meschter 1953) were found to
exert a great inÑuence on anthocyanin stability. Loss of
anthocyanins and/or formation of brown compounds in
strawberry and red raspberry products during storage
have been attributed to many factors such as pH and
acidity, phenolic compounds, sugars and sugar degradation products, oxygen, ascorbic acid, fruit maturity and
thawing time (Markakis et al 1957 ; Wrolstad et al 1970 ;
Abers and Wrolstad 1979 ; Spayd and Morris 1981 ;
Rommel et al 1990 ; Withy et al 1993).
The quality of the colour may inÑuence consumerÏs
acceptance. It is therefore essential that jam is prepared
and stored at a temperature which will maximise colour
stability. Nevertheless, as far as we are aware, no studies
have been done on this aspect.
The purpose of the present work was to determine
the inÑuence of the cultivar on red raspberry jam antho-
MATERIAL AND METHODS
Material
Samples of two red raspberry (Rubus idaeus) cultivars,
“ZevaÏ (Socovos, Albacete, Spain) and “HeritageÏ
(Nerpio, Albacete, Spain), at processing maturity, were
harvested on the August 1995. Half of the total fruit
harvested was processed in Hero SA, on the same day,
while the rest was immediately frozen (at [20¡C) in
about 3 kg lots and jam was manufactured after 24 h.
Prior to jam preparation, samples were removed from
the bags to allow semi-thawing. Jam was made under
the speciÐc conditions of the Industry in order to obtain
a Ðnal product that contains 450 g fruit kg~1, 2 g pectin
kg~1, 0É4 g citric acid kg~1 and a Ðnal sucrose concentration up to 63 ¡Brix. Fruit and sugar were mixed with
* To whom correspondence should be addressed.
Contract/grant sponsor : MEC-CSIC
Contract/grant sponsor : Hero Espan8 a SA
565
( 1998 Society of Chemical Industry. J Sci Food Agric 0022È5142/98/$17.50. Printed in Great Britain
566
pectin and citric acid, processed for 15 min at 78¡C
under vacuum (500 mmHg), heated at 92¡C and
allowed to cool down to 88¡C before Ðlling glass jars
(45 g). Glass jars were closed and cooled gradually with
water and kept in the dark, at three di†erent temperatures (20, 30 and 37¡C), for 6 months.
Anthocyanin extraction
Five grams of fruit (fresh or frozen) was extracted with
15 ml acetone, in order to produce pectin clotting, for
5 min at room temperature. The extract was Ðltered,
concentrated under vacuum (35¡C), and the residue
redissolved in 5 ml acidiÐed water (30 ml formic acid
litre~1), this aqueous solution was adsorbed onto a C
18
Sep-Pak cartridge (Waters Associates, Milford, MA,
USA). The cartridge was washed with 30 ml formic acid
litre~1, and the pigments were eluted with 30 ml formic
acid litre~1 of methanol. The methanolic extract was
concentrated and redissolved in a mixture of aqueous
50 ml formic acid litre~1 containing 150 ml methanol
litre~1 (1 ml) and Ðltered through a 0É45 lm Type
Millex HV 13 Millipore Ðlter (Millipore Corp, Bedford,
MA, USA) before HPLC analysis. Each jam (5 g) was
extracted by stirring with 75 ml of a methanol/acetic
acid/water (25 : 1 : 24) mixture, for 20 min at room temperature, as previously reported (Garc• a-Viguera et al
1997). All extractions were done in triplicate.
C Garc• a-V iguera et al
sample (20 ll) was analysed on a Lichrochart 100
RP-18 reversed-phase column (125 ] 4 mm, particle
size 5 lm) using a mobile phase of 50 ml formic acid
litre~1 (solvent A) and methanol (solvent B). Elution
was performed at a Ñow rate of 1 ml min~1 using a gradient starting with 150 ml methanol litre~1, increasing
to 300 ml methanol litre~1 at 15 min, isocratic elution
for 5 min and increasing to 950 ml methanol litre~1 at
25 min. Detection was achieved at 520 nm. All analyses
were done in triplicate and results expressed as mean
value. Reproducibility of the HPLC analyses was ca
^6%.
HPLC analysis of Ñavonols
The same equipment as mentioned before, for anthocyanin fruit analyses, was used. Each sample (20 ll) was
analysed on a Lichrosorb RP-18 (Merck, Darmstadt,
Germany) reversed-phase column (250 ] 4 mm, particle
size 5 lm), using the same mobile phase as mentioned
above. Elution was performed at a Ñow rate of
1 ml min~1 using a gradient starting with 200 ml methanol litre~1, increasing to 500 ml methanol litre~1 at
20 min, to 600 ml methanol litre~1 at 30 min and to
950 ml methanol litre~1 at 35 min. Detection was
achieved at 360 nm. All analyses were done in triplicate
and results expressed as the mean value. Reproducibility of the HPLC analyses was ca ^ 6%.
Flavonol extraction
Flavonoids identiÐcation and quantiÐcation
Fifty grams of fresh fruit was mixed with 200 ml of
methanol and homogenised with an Ultra-Turrax T25
(Jankel & Kunkel, IKA-Labortechnik, Germany). The
homogenate was Ðltered, 50 ml of the Ðltrate was mixed
with 20 ml of distilled water and concentrated under
vacuum (35¡C) up to 20 ml. The aqueous solution was
adsorbed onto a C Sep-Pak cartridge, following the
18
same method as with the anthocyanins but with nonacidiÐed solvents. All extractions were done in triplicate.
The di†erent compounds were characterised by chromatographic comparison with authentic standards
(cyanidin 3-rutinoside from Apin Chemicals (UK) and
the rest of anthocyanins provided by Dr Bridle (IFR,
Reading Laboratory, UK)). Kaempferol and quercetin
3-glucosides previously isolated in our laboratory, their
spectra recorded with the diode array detector, and by
their mobility on HPLC. All anthocyanins were quantiÐed as cyanidin 3-rutinoside due to the lack of a sufficient amount of other standards, and Ñavonol
derivatives as quercetin 3-glucoside and kaempferol 3glucoside. The total anthocyanins were calculated by
addition of the amounts of the anthocyanins detected in
each chromatogram.
HPLC analysis of anthocyanins
For fruit anthocyanin identiÐcation the same apparatus
as in Garc• a-Viguera et al (1997) was used. For jam
analysis a Merck-Hitachi L-6200 intelligent pump
(Darmstadt, Germany) chromatograph was used,
equipped with a Merck-Hitachi UV-VIS detector
L-4200 and auto-injector Merck-Hitachi AS-2000 A.
Chromatograms were recorded and processed on a
D-2500 Chromato-Integrator (Merck-Hitachi). Each
Titratable acidity, soluble solids and pH determination
Two grams of jam was stirred with 75 ml distilled water
during 15 min and acidity was determinated by titration with 0É1 M NaOH to pH 8, in a Crison auto-
567
Colour and anthocyanin stability of red raspberry jam
burette model 736 (Barcelona, Spain) and expressed as
grams of citric acid per 100 ml of extract, in accordance
with AOAC (1984).
Soluble solids concentration (¡Brix) and pH were
measured in an Atago 1T (Japan) refractometer at 20¡C
and a Crison micropH 2000 (Barcelona, Spain)
pHmeter with glass electrode, respectively.
“HeritageÏ (fresh B0É72 and frozen B0É70). Nevertheless, no signiÐcant variations were observed in this
parameter during storage at the three di†erent temperatures (20, 30 and 37¡C). The total soluble solids
showed a constant value (B65¡Brix) along the experiment for all the analysed jams. And no changes in pH
through storage were noticed (B3É33).
Colour measurements
A tristimulus colour spectrophotometer Minolta
CM-508i (Osaka, Japan) was used to obtain the absorption spectra from which L *a*b* values were calculated
using illuminant D65 and a 10¡ observer according to
the CIELAB 76 convention (McLaren 1980). Hue angle
(H) was calculated from H \ arctan b*/a*. Data were
recorded and processed on a Minolta ChromaControl
S, PC based colorimetric data system. All measures
were done in triplicate ; the mean values are reported in
the data.
RESULTS
Changes in titratable acidity (TA), soluble solids (ÄBrix)
and pH
TA was slightly higher for those jams elaborated with
Zeva cultivar (fresh B0É86 and frozen B0É81) than with
Anthocyanin composition of raspberry fruits and changes
during processing
The anthocyanins present in fresh raspberry fruits of
both cultivars (“ZevaÏ and “HeritageÏ) were analysed by
HPLC. Qualitative and quantitative di†erences were
found when analysing the two cultivars. While four cyanidin
based
anthocyanins
(3-sophoroside,
3glucosylrutinoside, 3-glucoside and 3-rutinoside) were
found in “ZevaÏ, fruit of the cultivar Heritage contained
only the 3-sophoroside and 3-glucoside. These results
were consistent with previously reported data on the
composition of Heritage cv (Francis 1972), although
nothing has been published, as far as we are aware, on
the anthocyanin composition in “ZevaÏ. Quantitative
data on the total anthocyanin content showed that
“ZevaÏ presented a higher amount (double than “HeritageÏ) of these pigments (Table 1). Cyanidin 3-glucoside
was the main pigment in cultivar Zeva, while in cultivar
Heritage this was cyanidin 3-sophoroside.
TABLE 1
Anthocyanin losses during red raspberry jam manufacturing (means ^ SD, n \ 3)a
Fresh fruit
(cv Zeva)
Frozen fruit
(cv Zeva)
Fresh fruit
(cv Heritage)
Frozen fruit
(cv Heritage)
339É91 (^40É59)
211É30 (^7É37)
293É03 (^34É99)
182É58 (^18É30)
596É61 (^4É50)
518É78 (^61É76)
515É75 (^20É74)
399É61 (^2É23)
99É92 (^11É37)
68É73 (^1É80)
86É14 (^9É80)
57É56 (^7É59)
ND
ND
ND
ND
Cy-3-glc
Fruit
Jam
941É77 (^103É14)
542É59 (^10É76)
811É87 (^88É91)
504É54 (^63É39)
464É16 (^34É77)
364É17 (^43É56)
375É68 (^1É93)
275É00 (^24É24)
Cy-3-rut
Fruit
Jam
444É42 (^54É98)
260É13 (13É64)
383É12 (^47É39)
235É85 (^36É85)
ND
ND
ND
ND
1826É02
1082É75
1574É16
980É53
1060É77
882É95
891É43
674É61
Cy-3-soph
Fruit
Jam
Cy-3-glc rut
Fruit
Jam
T otal
Fruit
Jam
a Values are micrograms of anthocyanins per gram of fruit in jam (fresh weight). HPLC reproducibility was ca ^6%. Cy 3-soph, Cyanidin 3-sophoroside ; Cy 3-glc-rut, Cyanidin 3-glucosyl
rutinoside ; Cy 3-glc, Cyanidin 3-glucoside ; Cy 3-rut, Cyanidin 3-rutinoside ; ND, non-detected.
568
C Garc• a-V iguera et al
when increasing temperature in all studied jams. The
higher loss in pigment composition, at 30 and 37¡C, was
observed during the Ðrst month, while jams stored at
20¡C showed a progressive decrease of anthocyanins
during the Ðrst 3 months (Figs 1 and 2). Some minor
di†erences in jams stored at 20¡C can also be pointed
out in this aspect, as jams made with “ZevaÏ (Fig 1)
showed an anthocyanin degradation rate slower than
those made with “HeritageÏ (Fig 2). Nevertheless, at the
end of the experiment the total anthocyanin content
was reduced down to 4È7% of the initial anthocyanins,
in all analysed jams.
It is also remarkable that cyanidin 3-glucoside, the
major pigment of “ZevaÏ, was the most unstable anthocyanin during jam processing and storage (Tables 2 and
3). This is in accordance with Rommel et al (1990) that
have reported that this pigment was more reactive and
therefore more likely to polymerise than other anthocyanins, with an associated increase in browning.
Nevertheless, the stability of this pigment was similar to
that of cyanidin 3-sophoroside in “HeritageÏ (Tables 4
and 5).
Fig 1. Total anthocyanin (=) and a* value (…) degradation
of red raspberry jams, made with Zeva variety, stored at 20,
30 and 37¡C. Black symbols represent jams prepared with
fresh fruit, white symbols represent frozen fruit.
During jam processing the total anthocyanin content
per gram of fruit (fresh weight) was reduced on a
17È24% when using “HeritageÏ, while the percentage of
loss increased to 37È40% when jams were prepared
with “ZevaÏ red raspberries (Table 1). Thawing resulted
in jam with a smaller anthocyanin content (9È24%
lower). This is not unexpected, since during freezing and
thawing, the cell structures are disrupted and the plastidic oxidative enzymes (polyphenol oxidases, PPO) and
the vacuolar substrates (phenolics) interact and during
thawing there is a loss of phenolic pigments due to this
enzymatic process.
Anthocyanin stability during jam storage
Storage temperature was the main responsible factor for
anthocyanin loss. Thus, the degradation rate increased
Fig 2. Total anthocyanin (=) and a* value (…) degradation
of red raspberry jams, made with Heritage variety, stored at
20, 30 and 37¡C. Black symbols represent jams prepared with
fresh fruit, white symbols represent frozen fruit.
569
Colour and anthocyanin stability of red raspberry jam
TABLE 2
Anthocyanins stability of red raspberry jam elaborated with fresh fruit (cv Zeva) during storage
at 20, 30 and 37¡C (mean ^ SD, n \ 3)a
Cy 3-soph
Cy 3-glc-rut
Cy 3-glc
Cy 3-rut
Initial
211É30 (^7É37)
68É73 (^1É80)
542É59 (^10É75)
260É13 (^13É64)
Days at 20¡C
32
62
95
108
123
139
159
179
188
126É17
82É84
31É09
21É29
19É00
18É75
19É82
18É55
18É82
(^9É33)
(^2É17)
(^6É69)
(^0É60)
(^0É18)
(^0É36)
(^0É87)
(^0É64)
(^0É84)
53É79
33É49
9É09
9É51
8É42
8É02
8É91
8É49
8É31
(^9É47)
(^0É27)
(^1É84)
(^0É29)
(^0É31)
(^0É71)
(^0É24)
(^0É33)
(^0É20)
314É04
188É71
67É99
44É02
36É24
35É31
34É26
32É26
30É11
(^64É88)
(^3É60)
(^17É31)
(^0É87)
(^0É49)
(^1É07)
(^0É16)
(^1É18)
(^1É89)
171É21
97É19
34É75
23É26
19É66
20É02
20É15
19É09
18É89
(^27É78)
(^1É71)
(^7É98)
(^0É82)
(^0É53)
(^0É67)
(^0É02)
(^0É11)
(^0É93)
Days at 30¡C
32
62
95
108
123
139
73É30
23É95
4É78
5É24
2É31
1É42
(^5É69)
(^4É47)
(^0É09)
(^0É98)
(^0É18)
(^0É38)
30É62
12É07
2É96
3É36
1É33
0É84
(^2É64)
(^2É02)
(^0É20)
(^0É73)
(^0É16)
(^0É13)
152É56
40É06
7É73
8É11
3É64
2É07
(^14É11)
(^8É78)
(^0É78)
(^1É36)
(^0É27)
(^0É56)
87É32
25É95
5É18
5É82
2É13
1É29
(^9É13)
(^4É84)
(^0É60)
(^1É16)
(^0É18)
(^0É27)
Days at 37¡C
32
62
95
35É53 (^13É00)
6É31 (^0É58)
3É60 (^0É09)
16É80 (^5É75)
3É60 (^0É56)
1É78 (^0É20)
61É22 (^22É93)
8É80 (^0É73)
6É55 (^0É78)
39É75 (^15É02)
6É58 (^0É71)
3É98 (^0É60)
a Values are microgram of anthocyanin per gram of fruit in jam (fresh weight). HPLC reproducibility was ca ^6%. Cy 3-soph, Cyanidin 3-sophoroside ; Cy 3-glc-rut, Cyanidin 3-glucosyl
rutinoside ; Cy 3-glc, Cyanidin 3-glucoside ; Cy 3-rut, Cyanidin 3-rutinoside ; ND, non-detected.
Jam prepared with frozen fruit presented a similar
degradation slope than that made with fresh fruit (Figs
1 and 2).
Colour quality alteration
It is important to mention that while all the previous
changes were noticed in anthocyanin concentration,
only minor changes were found when analysing the
colour of these products stored at 20¡C measured with
a reÑectance spectrophotometer. Thereby, no signiÐcant
di†erences where noticed when analysing the L * value,
for the two cultivars and for jams made with fresh or
frozen fruit, or even during the storage at the di†erent
temperatures (Table 6), indicating no changes in lightness. A higher decrease in a* value was detected when
jam was stored at higher temperatures. This e†ect being
more remarkable in “HeritageÏ than in “ZevaÏ, due to the
fact that “HeritageÏ presented an initial a* value higher
than “ZevaÏ, while the decrease was higher in that Ðrst
cultivar reaching the same value at the end of the
experiment. On the other hand, only minor di†erences
were observed in b* values. However, changes in a* and
b* values showed that the H value variations were more
important for those jams made with frozen fruit and/or
Heritage variety and stored at higher temperatures,
indicating an increase in browning. Thus, when jams
were stored at 20¡C no signiÐcant di†erences were
observed in comparison with those products made with
Zeva cultivar or fresh fruit.
Flavonol composition of raspberry fruits and changes
during processing
In contrast with results obtained when analysing anthocyanin composition, only quantitative di†erences were
found between both raspberry varieties when Ñavonol
composition was studied. Quercetin 3-glucoside plus 3glucuronide (co-eluting under our conditions) and
kaempferol 3-glucoside and 3-glucuronide (also coeluting) were detected (Table 7), in accordance with previous Ðndings in red raspberry juice (Rommel and
Wrolstad, 1993). It is also remarkable that quercetin 3glycoside presents a high stability during processing as
570
C Garc• a-V iguera et al
TABLE 3
Anthocyanins stability of red raspberry jam elaborated with frozen fruit (cv Zeva) during storage
at 20, 30 and 37¡Ca
Cy 3-soph
Cy 3-glc-rut
Cy 3-glc
Cy 3-rut
Initial
182É58 (^18É30)
57É56 (^7É59)
504É54 (^63É39)
235É85 (^36É85)
Days at 20¡C
32
62
95
108
123
139
159
179
188
129É81
77É53
32É71
27É35
16É64
16É47
13É73
15É64
13É47
(^12É71)
(^7É35)
(^0É80)
(^2É69)
(^0É71)
(^1É42)
(^1É69)
(^0É64)
(^3É98)
47É46
30É80
8É82
8É09
7É47
7É31
6É31
6É13
3É62
(^3É47)
(^2É36)
(^0É04)
(^0É69)
(^0É11)
(^0É51)
(^0É80)
(^0É42)
(^0É02)
328É77
173É16
74É81
58É57
33É06
30É33
23É93
24É22
24É46
(^35É66)
(^17É66)
(^3É18)
(^8É11)
(^1É53)
(^2É22)
(^2É87)
(^1É47)
(^1É02)
163É56
89É12
36É49
22É62
19É09
17É35
13É58
12É53
12É15
(^14É44)
(^7É75)
(^1É12)
(^4É71)
(^0É76)
(^1É82)
(^1É69)
(^0É84)
(^0É60)
Days at 30¡C
32
62
95
108
123
139
72É17
28É75
5É40
4É49
2É69
1É67
(^9É78)
(^4É38)
(^0É51)
(^0É49)
(^1É33)
(^0É36)
28É29
13É89
2É98
2É87
1É38
0É82
(^3É22)
(^1É98)
(^0É49)
(^0É20)
(^0É69)
(^0É16)
157É16
48É75
8É27
7É31
4É22
2É42
(^18É02)
(^7É27)
(^1É44)
(^0É49)
(^2É04)
(^0É38)
83É35
30É60
5É29
4É89
2É47
1É47
(^7É60)
(^4É67)
(^0É13)
(^0É62)
(^1É29)
(^0É22)
Days at 37¡C
32
62
23É18 (^1É47)
4É82 (^1É00)
11É02 (^0É76)
2É64 (^0É64)
40É93 (^2É91)
7É31 (^0É84)
25É04 (^2É58)
5É75 (^1É47)
a Values are expressed as in Table 2.
TABLE 4
Anthocyanins stability of red raspberry jam elaborated with
fresh fruit (cv Heritage) during storage at 20, 30 and 37¡Ca
Cy 3-soph
Cy 3-glc
Initial
518É78 (^61É76)
364É17 (^43É56)
Days at 20¡C
31
53
88
106
120
139
155
175
191
308É70
125É48
77É77
74É84
65É28
60É04
39É82
36É82
28É22
(^56É51)
(^15É22)
(^15É20)
(^4É29)
(^8É89)
(^5É56)
(^7É04)
(^6É09)
(^3É42)
182É38
70É64
42É48
33É40
32É02
27É75
11É75
10É84
10É29
(^33É51)
(^8É80)
(^8É20)
(^3É58)
(^11É71)
(^2É51)
(^1É60)
(^0É33)
(^0É60)
Days at 30¡C
31
53
88
106
120
139
189É07
43É62
17É11
16É58
15É27
11É84
(^47É80)
(^4É29)
(^1É36)
(^0É09)
(^2É62)
(^0É20)
96É63
18É49
6É15
5É82
4É73
4É16
(^24É73)
(^2É29)
(^0É62)
(^0É11)
(^0É69)
(^0É16)
Days at 37¡C
31
53
105É94 (^12É69)
6É20 (^1É04)
the content of this Ñavonoid per gram of fruit was
reduced only on a ^ 6% for both varieties, while when
kaempferol 3-glycoside is considered the content is
reduced on a ^22% (Table 7).
DISCUSSION
a Values are expressed as in Table 2.
49É80 (^4É53)
1É51 (^0É47)
The results obtained with jams stored at di†erent temperatures are in accordance with previous reports on
other food products (Spayd and Morris 1981 ; Withy et
al 1993). Thus, the stability of anthocyanins and the rate
of their degradation is markedly inÑuenced by temperature, and formation of chalcone form is favoured by
increasing temperature, during storage and processing,
at the expense of the other species (Markakis 1982 ;
Jackman and Smith 1996). It has also been demonstrated that the concentration of polymeric pigments
increase with temperature and storage time, and this
has an important inÑuence in the colouration of juices
and red wines (Somers 1971 ; Adams and Ongley 1973 ;
Bakker and Timberlake 1986 ; Withy et al 1993). In this
aspect it is remarkable that the rate of colour loss is
much slower than the rate of anthocyanin degradation
(Figs 1 and 2).
Although the expression of anthocyanin colour is well
known to be pH dependent (Brouillard 1982) these jams
571
Colour and anthocyanin stability of red raspberry jam
TABLE 5
Anthocyanins stability of red raspberry jam elaborated with
frozen fruit (cv Heritage) during storage at 20, 30 and 37¡Ca
Initial
Cy 3-soph
Cy 3-glc
399É56 (^42É22)
274É97 (^24É24)
Days at 20¡C
31
53
88
106
120
139
155
175
191
292É88
106É10
52É51
48É82
47É22
45É46
25É75
24É62
21É82
(^19É06)
(^3É36)
(^3É84)
(^9É67)
(^3É31)
(^1É22)
(^1É31)
(^0É89)
(^4É64)
167É89
57É75
24É71
22É60
20É89
20É49
9É00
7É84
7É09
(^6É75)
(^2É20)
(^1É31)
(^4É27)
(^0É31)
(^1É22)
(^0É60)
(^1É82)
(^0É31)
Days at 30¡C
31
53
88
106
120
139
136É28
43É57
10É02
8É67
8É44
3É73
(^26É35)
(^0É27)
(^0É04)
(^0É20)
(^0É91)
(^0É76)
69É06
15É20
2É87
2É47
2É60
1É38
(^10É87)
(^0É20)
(^0É01)
(^0É47)
(^0É44)
(^0É62)
Days at 37¡C
31
53
74É79 (^14É09)
9É22 (^2É64)
31É82 (^6É89)
2É82 (^1É64)
a Values are expressed as in Table 2.
TABLE 7
Flavonol losses during red raspberry jam manufacturing
(mean ^ SD, n\3)a
Quer 3-gly
Fruit
Jam
Kaemp 3-gly
Fruit
Jam
Frozen fruit
(cv Zeva)
Frozen fruit
(cv Heritage)
33É79 (^2É27)
31É79 (^2É51)
52É65 (^3É17)
50É02 (^4É23)
7É14 (^0É68)
5É73 (^0É90)
7É17 (^0É69)
5É74 (^0É88)
a Values are micrograms of Ñavonoids per gram of fruit in jam
(fresh weight). HPLC reproducibility was ca ^6%. Quer
3-gly, Quercetin 3-glycoside ; Kaemp 3-gly, Kaempferol 3glycoside.
fell within a narrow pH range from 3É22 to 3É46, averaging 3É33, and thus, pH was not a signiÐcant factor in
colour expression in these jams. Therefore, other factors
may have a signiÐcant role in the expression of colour
in raspberry jams by co-pigmentation or some other
physicochemical processes. In addition to anthocyanin,
it has been reported that red raspberries also contain
high concentrations of phenolic acids (Schwab and
Herrmann 1985), Ñavonols (Henning 1981) and Ñavan3-ols (Mossel and Herrmann 1974), which are known to
TABLE 6
L *a*b and Hue angle values obtained for red raspberry jams prepared with fresh or
frozen fruit
Zeva fresh
Zeva frozen
Heritage fresh
Heritage frozen
L*
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
32É73
34É69
34É27
30É92
(^0É94)
(^1É70)
(^0É42)
(^0É43)
33É78
36É01
34É54
30É82
(^0É24)
(^1É68)
(^0É27)
(^0É32)
36É30
41É69
40É74
35É04
(^0É27)
(^1É64)
(^0É30)
(^1É22)
37É36
43É20
40É88
38É25
(^0É09)
(^1É28)
(^0É17)
(^0É53)
a*
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
31É63
18É53
23É48
24É28
(^2É03)
(^1É52)
(^0É60)
(^1É56)
33É04
19É42
22É50
23É25
(^0É31)
(^1É30)
(^0É97)
(^0É92)
36É65
17É32
25É01
30É46
(^0É42)
(^0É62)
(^0É17)
(^2É22)
37É42
16É75
21É15
29É89
(^0É52)
(^0É47)
(^0É30)
(^0É33)
b*
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
13É79
15É24
13É60
9É85
(^1É50)
(^2É36)
(^0É51)
(^0É68)
15É10
16É35
14É11
9É78
(^0É34)
(^0É47)
(^0É30)
(^0É61)
18É29
22É74
18É47
14É78
(^0É23)
(^1É24)
(^0É35)
(^1É07)
19É16
24É69
20É29
17É34
(^0É40)
(^1É70)
(^0É39)
(^0É34)
H
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
23É55
39É53
30É08
22É07
(^0É64)
(^1É00)
(^0É70)
(^0É41)
24É56
40É09
32É09
22É82
(^0É83)
(^0É35)
(^0É30)
(^0É59)
26É52
52É71
36É44
25É88
(^0É50)
(^1É11)
(^1É12)
(^0É45)
27É12
55É84
43É81
30É12
(^0É66)
(^1É30)
(^0É92)
(^0É88)
Data obtained initially (day 0) and at the end of the experiment, at the di†erent temperatures (day 108 at 37¡C, day 139 at 30¡C and day 207 at 20¡C). Standard Deviation in
brackets.
572
C Garc• a-V iguera et al
interact with anthocyanins to produce an increase in
colour intensity and a bathocromic shift in the spectrum
of the anthocyanin to give purple to blue colours
(Francis 1975 ; Mazza and Brouillard 1990 ; Garc• aViguera et al 1994 ; Rivas-Gonzalo et al 1995). All previous studies have been done in liquid solutions (juices,
wines or model system). Nevertheless, it may be
assumed that the same reactions take place in jams even
if the bathocromic shift is not as evident as in liquid
media and no precipitation is shown, due to the formation of polymers.
Zeva cultivar presented a higher monomericanthocyanin amount but “HeritageÏ a* value was higher
during the experiment, conÐrming that the monomeric
species are not the main factor in colour expression.
This may be explained, partially, if the concentration of
Ñavonols is considered, as colour is the result of the
physical interaction of electrons between the anthocyanin and co-pigments rings within the anthocyanin/
co-pigment complex, and Ñavonols have proved to be
the most efficient co-pigments (Mazza and Miniati
1993). When the Ñavonol composition of both varieties
was analysed quercetin and kaempferol 3-glycosides
(glucoside plus glucoronide co-eluting) were found
(Table 7). Nevertheless, “ZevaÏ presented a lower concentration, of quercetin 3-glycoside (33É79 lg g~1 fresh
fruit), than “HeritageÏ (52É65 lg g~1), while both varieties contained similar amounts of kaempferol 3glycoside (7É14 lg g~1 and 7É17 lg g~1, respectively).
Moreover, during processing only ^ 6% of quercetin
3-glycoside was lost (Table 7) ; therefore, a considerable
amount of this Ñavonol is present in the jams. Quercetin
derivatives are well known co-pigments (Mazza and
Miniati 1993). Thus, the di†erences found in this copigment concentration could explain the higher red hue
found for “HeritageÏ at the beginning of the assay, but
not at the end of each experiment, when total anthocyanin concentration had decreased to less than ^ 10%
of the initial value. Therefore, the di†erences found in
colour, during storage, are more likely to be due to polymerisation phenomena, similar to what was mentioned
above for wines or juices.
It can also be concluded that the colour of processed
and stored at 20¡C products is not signiÐcantly a†ected
by freezing for 24 h. Moreover, although total anthocyanin concentration is lower when jam was made with
frozen fruit, the rate of loss of these compounds during
storage was not inÑuenced by this factor. Nevertheless,
the development of browning was higher when jams
were produced with frozen fruit and stored at higher
temperatures.
ACKNOWLEDGEMENTS
CGV wish to thank the Spanish Ministerio de Educacion y Ciencia, via CSIC, for a contract and PZ to Hero
Espan8 a SA for a grant. Thanks also to C Mart• nez Ataz
for technical assistance.
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and other factors on strawberry products. J Agric Food
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Mossel H D, Herrmann K 1974 Die phenolischen Inhaltssto†e des Obstes. IV. Die phenolishen inhaltssto†e der
brombeeren und himbeeren und deren veranderugen
wahrend Wachstum und reife der Frutche. Z L ebemns
Unters Forsch 154 324È327.
Pilano L S, Wrolstad R E, Heatherbell D A 1985 InÑuence of
fruit composition, maturity and mold concentration on the
Colour and anthocyanin stability of red raspberry jam
colour and appearance of strawberry wine. J Food Sci 50
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red raspberry juice as inÑuenced by cultivar, processing and
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Spayd S E, Morris J R 1981 InÑuence of immature fruits on
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448È452.
Colour and Anthocyanin Stability of Red
Raspberry Jam
Cristina Garc• a-Viguera,1* Pilar Zafrilla,1 Francisco Arte s,1 Fernando Romero,2
Pedro Abella n2 and Francisco A Toma s-Barbera n1
1 Dpto Ciencia y Tecnolog• a de Alimentos, CEBAS-CSIC, PO Box 4195, 30080, Murcia, Spain
2 Dpto de Calidad y Desarrollo, Hero Espan8 a, SA Alcantarilla, Spain
(Received 3 November 1997 ; revised version received 23 February 1998 ; accepted 6 April 1998)
Abstract : Anthocyanin and colour stability of red raspberry jams made from two
di†erent varieties (“ZevaÏ and “HeritageÏ) were analysed during 6 months, stored
at three temperatures (20, 30 and 37¡C). Also the inÑuence of freezing the fruit,
previously to jam manufacture, was evaluated. Di†erent anthocyanin composition was detected for both cultivars and while “ZevaÏ fruit had a higher total
anthocyanin content, Heritage variety produced jams with a higher redness hue.
The development of browning was directly related to storage temperature but
not to thawing or the variety of fruit used. ( 1998 Society of Chemical Industry.
J Sci Food Agric 78, 565È573 (1998)
Key words : raspberry ; jams ; anthocyanins ; cultivar ; colour ; storage ; stability
cyanin composition and stability, and to deÐne the
changes in colour and pigment composition which may
occur during processing and storage at di†erent temperatures for 6 months. The inÑuence of freezing the
fruit previously to jam manufacture was also examined
as pigment degradation may take place during thawing.
INTRODUCTION
Colour stability of red fruit or red fruit products is
inÑuenced by many factors which have been previously
reported (Markakis 1982). Temperature and time of
processing (Decareu et al 1956 ; Markakis 1982 ; Pilano
et al 1985) and storage (Meschter 1953) were found to
exert a great inÑuence on anthocyanin stability. Loss of
anthocyanins and/or formation of brown compounds in
strawberry and red raspberry products during storage
have been attributed to many factors such as pH and
acidity, phenolic compounds, sugars and sugar degradation products, oxygen, ascorbic acid, fruit maturity and
thawing time (Markakis et al 1957 ; Wrolstad et al 1970 ;
Abers and Wrolstad 1979 ; Spayd and Morris 1981 ;
Rommel et al 1990 ; Withy et al 1993).
The quality of the colour may inÑuence consumerÏs
acceptance. It is therefore essential that jam is prepared
and stored at a temperature which will maximise colour
stability. Nevertheless, as far as we are aware, no studies
have been done on this aspect.
The purpose of the present work was to determine
the inÑuence of the cultivar on red raspberry jam antho-
MATERIAL AND METHODS
Material
Samples of two red raspberry (Rubus idaeus) cultivars,
“ZevaÏ (Socovos, Albacete, Spain) and “HeritageÏ
(Nerpio, Albacete, Spain), at processing maturity, were
harvested on the August 1995. Half of the total fruit
harvested was processed in Hero SA, on the same day,
while the rest was immediately frozen (at [20¡C) in
about 3 kg lots and jam was manufactured after 24 h.
Prior to jam preparation, samples were removed from
the bags to allow semi-thawing. Jam was made under
the speciÐc conditions of the Industry in order to obtain
a Ðnal product that contains 450 g fruit kg~1, 2 g pectin
kg~1, 0É4 g citric acid kg~1 and a Ðnal sucrose concentration up to 63 ¡Brix. Fruit and sugar were mixed with
* To whom correspondence should be addressed.
Contract/grant sponsor : MEC-CSIC
Contract/grant sponsor : Hero Espan8 a SA
565
( 1998 Society of Chemical Industry. J Sci Food Agric 0022È5142/98/$17.50. Printed in Great Britain
566
pectin and citric acid, processed for 15 min at 78¡C
under vacuum (500 mmHg), heated at 92¡C and
allowed to cool down to 88¡C before Ðlling glass jars
(45 g). Glass jars were closed and cooled gradually with
water and kept in the dark, at three di†erent temperatures (20, 30 and 37¡C), for 6 months.
Anthocyanin extraction
Five grams of fruit (fresh or frozen) was extracted with
15 ml acetone, in order to produce pectin clotting, for
5 min at room temperature. The extract was Ðltered,
concentrated under vacuum (35¡C), and the residue
redissolved in 5 ml acidiÐed water (30 ml formic acid
litre~1), this aqueous solution was adsorbed onto a C
18
Sep-Pak cartridge (Waters Associates, Milford, MA,
USA). The cartridge was washed with 30 ml formic acid
litre~1, and the pigments were eluted with 30 ml formic
acid litre~1 of methanol. The methanolic extract was
concentrated and redissolved in a mixture of aqueous
50 ml formic acid litre~1 containing 150 ml methanol
litre~1 (1 ml) and Ðltered through a 0É45 lm Type
Millex HV 13 Millipore Ðlter (Millipore Corp, Bedford,
MA, USA) before HPLC analysis. Each jam (5 g) was
extracted by stirring with 75 ml of a methanol/acetic
acid/water (25 : 1 : 24) mixture, for 20 min at room temperature, as previously reported (Garc• a-Viguera et al
1997). All extractions were done in triplicate.
C Garc• a-V iguera et al
sample (20 ll) was analysed on a Lichrochart 100
RP-18 reversed-phase column (125 ] 4 mm, particle
size 5 lm) using a mobile phase of 50 ml formic acid
litre~1 (solvent A) and methanol (solvent B). Elution
was performed at a Ñow rate of 1 ml min~1 using a gradient starting with 150 ml methanol litre~1, increasing
to 300 ml methanol litre~1 at 15 min, isocratic elution
for 5 min and increasing to 950 ml methanol litre~1 at
25 min. Detection was achieved at 520 nm. All analyses
were done in triplicate and results expressed as mean
value. Reproducibility of the HPLC analyses was ca
^6%.
HPLC analysis of Ñavonols
The same equipment as mentioned before, for anthocyanin fruit analyses, was used. Each sample (20 ll) was
analysed on a Lichrosorb RP-18 (Merck, Darmstadt,
Germany) reversed-phase column (250 ] 4 mm, particle
size 5 lm), using the same mobile phase as mentioned
above. Elution was performed at a Ñow rate of
1 ml min~1 using a gradient starting with 200 ml methanol litre~1, increasing to 500 ml methanol litre~1 at
20 min, to 600 ml methanol litre~1 at 30 min and to
950 ml methanol litre~1 at 35 min. Detection was
achieved at 360 nm. All analyses were done in triplicate
and results expressed as the mean value. Reproducibility of the HPLC analyses was ca ^ 6%.
Flavonol extraction
Flavonoids identiÐcation and quantiÐcation
Fifty grams of fresh fruit was mixed with 200 ml of
methanol and homogenised with an Ultra-Turrax T25
(Jankel & Kunkel, IKA-Labortechnik, Germany). The
homogenate was Ðltered, 50 ml of the Ðltrate was mixed
with 20 ml of distilled water and concentrated under
vacuum (35¡C) up to 20 ml. The aqueous solution was
adsorbed onto a C Sep-Pak cartridge, following the
18
same method as with the anthocyanins but with nonacidiÐed solvents. All extractions were done in triplicate.
The di†erent compounds were characterised by chromatographic comparison with authentic standards
(cyanidin 3-rutinoside from Apin Chemicals (UK) and
the rest of anthocyanins provided by Dr Bridle (IFR,
Reading Laboratory, UK)). Kaempferol and quercetin
3-glucosides previously isolated in our laboratory, their
spectra recorded with the diode array detector, and by
their mobility on HPLC. All anthocyanins were quantiÐed as cyanidin 3-rutinoside due to the lack of a sufficient amount of other standards, and Ñavonol
derivatives as quercetin 3-glucoside and kaempferol 3glucoside. The total anthocyanins were calculated by
addition of the amounts of the anthocyanins detected in
each chromatogram.
HPLC analysis of anthocyanins
For fruit anthocyanin identiÐcation the same apparatus
as in Garc• a-Viguera et al (1997) was used. For jam
analysis a Merck-Hitachi L-6200 intelligent pump
(Darmstadt, Germany) chromatograph was used,
equipped with a Merck-Hitachi UV-VIS detector
L-4200 and auto-injector Merck-Hitachi AS-2000 A.
Chromatograms were recorded and processed on a
D-2500 Chromato-Integrator (Merck-Hitachi). Each
Titratable acidity, soluble solids and pH determination
Two grams of jam was stirred with 75 ml distilled water
during 15 min and acidity was determinated by titration with 0É1 M NaOH to pH 8, in a Crison auto-
567
Colour and anthocyanin stability of red raspberry jam
burette model 736 (Barcelona, Spain) and expressed as
grams of citric acid per 100 ml of extract, in accordance
with AOAC (1984).
Soluble solids concentration (¡Brix) and pH were
measured in an Atago 1T (Japan) refractometer at 20¡C
and a Crison micropH 2000 (Barcelona, Spain)
pHmeter with glass electrode, respectively.
“HeritageÏ (fresh B0É72 and frozen B0É70). Nevertheless, no signiÐcant variations were observed in this
parameter during storage at the three di†erent temperatures (20, 30 and 37¡C). The total soluble solids
showed a constant value (B65¡Brix) along the experiment for all the analysed jams. And no changes in pH
through storage were noticed (B3É33).
Colour measurements
A tristimulus colour spectrophotometer Minolta
CM-508i (Osaka, Japan) was used to obtain the absorption spectra from which L *a*b* values were calculated
using illuminant D65 and a 10¡ observer according to
the CIELAB 76 convention (McLaren 1980). Hue angle
(H) was calculated from H \ arctan b*/a*. Data were
recorded and processed on a Minolta ChromaControl
S, PC based colorimetric data system. All measures
were done in triplicate ; the mean values are reported in
the data.
RESULTS
Changes in titratable acidity (TA), soluble solids (ÄBrix)
and pH
TA was slightly higher for those jams elaborated with
Zeva cultivar (fresh B0É86 and frozen B0É81) than with
Anthocyanin composition of raspberry fruits and changes
during processing
The anthocyanins present in fresh raspberry fruits of
both cultivars (“ZevaÏ and “HeritageÏ) were analysed by
HPLC. Qualitative and quantitative di†erences were
found when analysing the two cultivars. While four cyanidin
based
anthocyanins
(3-sophoroside,
3glucosylrutinoside, 3-glucoside and 3-rutinoside) were
found in “ZevaÏ, fruit of the cultivar Heritage contained
only the 3-sophoroside and 3-glucoside. These results
were consistent with previously reported data on the
composition of Heritage cv (Francis 1972), although
nothing has been published, as far as we are aware, on
the anthocyanin composition in “ZevaÏ. Quantitative
data on the total anthocyanin content showed that
“ZevaÏ presented a higher amount (double than “HeritageÏ) of these pigments (Table 1). Cyanidin 3-glucoside
was the main pigment in cultivar Zeva, while in cultivar
Heritage this was cyanidin 3-sophoroside.
TABLE 1
Anthocyanin losses during red raspberry jam manufacturing (means ^ SD, n \ 3)a
Fresh fruit
(cv Zeva)
Frozen fruit
(cv Zeva)
Fresh fruit
(cv Heritage)
Frozen fruit
(cv Heritage)
339É91 (^40É59)
211É30 (^7É37)
293É03 (^34É99)
182É58 (^18É30)
596É61 (^4É50)
518É78 (^61É76)
515É75 (^20É74)
399É61 (^2É23)
99É92 (^11É37)
68É73 (^1É80)
86É14 (^9É80)
57É56 (^7É59)
ND
ND
ND
ND
Cy-3-glc
Fruit
Jam
941É77 (^103É14)
542É59 (^10É76)
811É87 (^88É91)
504É54 (^63É39)
464É16 (^34É77)
364É17 (^43É56)
375É68 (^1É93)
275É00 (^24É24)
Cy-3-rut
Fruit
Jam
444É42 (^54É98)
260É13 (13É64)
383É12 (^47É39)
235É85 (^36É85)
ND
ND
ND
ND
1826É02
1082É75
1574É16
980É53
1060É77
882É95
891É43
674É61
Cy-3-soph
Fruit
Jam
Cy-3-glc rut
Fruit
Jam
T otal
Fruit
Jam
a Values are micrograms of anthocyanins per gram of fruit in jam (fresh weight). HPLC reproducibility was ca ^6%. Cy 3-soph, Cyanidin 3-sophoroside ; Cy 3-glc-rut, Cyanidin 3-glucosyl
rutinoside ; Cy 3-glc, Cyanidin 3-glucoside ; Cy 3-rut, Cyanidin 3-rutinoside ; ND, non-detected.
568
C Garc• a-V iguera et al
when increasing temperature in all studied jams. The
higher loss in pigment composition, at 30 and 37¡C, was
observed during the Ðrst month, while jams stored at
20¡C showed a progressive decrease of anthocyanins
during the Ðrst 3 months (Figs 1 and 2). Some minor
di†erences in jams stored at 20¡C can also be pointed
out in this aspect, as jams made with “ZevaÏ (Fig 1)
showed an anthocyanin degradation rate slower than
those made with “HeritageÏ (Fig 2). Nevertheless, at the
end of the experiment the total anthocyanin content
was reduced down to 4È7% of the initial anthocyanins,
in all analysed jams.
It is also remarkable that cyanidin 3-glucoside, the
major pigment of “ZevaÏ, was the most unstable anthocyanin during jam processing and storage (Tables 2 and
3). This is in accordance with Rommel et al (1990) that
have reported that this pigment was more reactive and
therefore more likely to polymerise than other anthocyanins, with an associated increase in browning.
Nevertheless, the stability of this pigment was similar to
that of cyanidin 3-sophoroside in “HeritageÏ (Tables 4
and 5).
Fig 1. Total anthocyanin (=) and a* value (…) degradation
of red raspberry jams, made with Zeva variety, stored at 20,
30 and 37¡C. Black symbols represent jams prepared with
fresh fruit, white symbols represent frozen fruit.
During jam processing the total anthocyanin content
per gram of fruit (fresh weight) was reduced on a
17È24% when using “HeritageÏ, while the percentage of
loss increased to 37È40% when jams were prepared
with “ZevaÏ red raspberries (Table 1). Thawing resulted
in jam with a smaller anthocyanin content (9È24%
lower). This is not unexpected, since during freezing and
thawing, the cell structures are disrupted and the plastidic oxidative enzymes (polyphenol oxidases, PPO) and
the vacuolar substrates (phenolics) interact and during
thawing there is a loss of phenolic pigments due to this
enzymatic process.
Anthocyanin stability during jam storage
Storage temperature was the main responsible factor for
anthocyanin loss. Thus, the degradation rate increased
Fig 2. Total anthocyanin (=) and a* value (…) degradation
of red raspberry jams, made with Heritage variety, stored at
20, 30 and 37¡C. Black symbols represent jams prepared with
fresh fruit, white symbols represent frozen fruit.
569
Colour and anthocyanin stability of red raspberry jam
TABLE 2
Anthocyanins stability of red raspberry jam elaborated with fresh fruit (cv Zeva) during storage
at 20, 30 and 37¡C (mean ^ SD, n \ 3)a
Cy 3-soph
Cy 3-glc-rut
Cy 3-glc
Cy 3-rut
Initial
211É30 (^7É37)
68É73 (^1É80)
542É59 (^10É75)
260É13 (^13É64)
Days at 20¡C
32
62
95
108
123
139
159
179
188
126É17
82É84
31É09
21É29
19É00
18É75
19É82
18É55
18É82
(^9É33)
(^2É17)
(^6É69)
(^0É60)
(^0É18)
(^0É36)
(^0É87)
(^0É64)
(^0É84)
53É79
33É49
9É09
9É51
8É42
8É02
8É91
8É49
8É31
(^9É47)
(^0É27)
(^1É84)
(^0É29)
(^0É31)
(^0É71)
(^0É24)
(^0É33)
(^0É20)
314É04
188É71
67É99
44É02
36É24
35É31
34É26
32É26
30É11
(^64É88)
(^3É60)
(^17É31)
(^0É87)
(^0É49)
(^1É07)
(^0É16)
(^1É18)
(^1É89)
171É21
97É19
34É75
23É26
19É66
20É02
20É15
19É09
18É89
(^27É78)
(^1É71)
(^7É98)
(^0É82)
(^0É53)
(^0É67)
(^0É02)
(^0É11)
(^0É93)
Days at 30¡C
32
62
95
108
123
139
73É30
23É95
4É78
5É24
2É31
1É42
(^5É69)
(^4É47)
(^0É09)
(^0É98)
(^0É18)
(^0É38)
30É62
12É07
2É96
3É36
1É33
0É84
(^2É64)
(^2É02)
(^0É20)
(^0É73)
(^0É16)
(^0É13)
152É56
40É06
7É73
8É11
3É64
2É07
(^14É11)
(^8É78)
(^0É78)
(^1É36)
(^0É27)
(^0É56)
87É32
25É95
5É18
5É82
2É13
1É29
(^9É13)
(^4É84)
(^0É60)
(^1É16)
(^0É18)
(^0É27)
Days at 37¡C
32
62
95
35É53 (^13É00)
6É31 (^0É58)
3É60 (^0É09)
16É80 (^5É75)
3É60 (^0É56)
1É78 (^0É20)
61É22 (^22É93)
8É80 (^0É73)
6É55 (^0É78)
39É75 (^15É02)
6É58 (^0É71)
3É98 (^0É60)
a Values are microgram of anthocyanin per gram of fruit in jam (fresh weight). HPLC reproducibility was ca ^6%. Cy 3-soph, Cyanidin 3-sophoroside ; Cy 3-glc-rut, Cyanidin 3-glucosyl
rutinoside ; Cy 3-glc, Cyanidin 3-glucoside ; Cy 3-rut, Cyanidin 3-rutinoside ; ND, non-detected.
Jam prepared with frozen fruit presented a similar
degradation slope than that made with fresh fruit (Figs
1 and 2).
Colour quality alteration
It is important to mention that while all the previous
changes were noticed in anthocyanin concentration,
only minor changes were found when analysing the
colour of these products stored at 20¡C measured with
a reÑectance spectrophotometer. Thereby, no signiÐcant
di†erences where noticed when analysing the L * value,
for the two cultivars and for jams made with fresh or
frozen fruit, or even during the storage at the di†erent
temperatures (Table 6), indicating no changes in lightness. A higher decrease in a* value was detected when
jam was stored at higher temperatures. This e†ect being
more remarkable in “HeritageÏ than in “ZevaÏ, due to the
fact that “HeritageÏ presented an initial a* value higher
than “ZevaÏ, while the decrease was higher in that Ðrst
cultivar reaching the same value at the end of the
experiment. On the other hand, only minor di†erences
were observed in b* values. However, changes in a* and
b* values showed that the H value variations were more
important for those jams made with frozen fruit and/or
Heritage variety and stored at higher temperatures,
indicating an increase in browning. Thus, when jams
were stored at 20¡C no signiÐcant di†erences were
observed in comparison with those products made with
Zeva cultivar or fresh fruit.
Flavonol composition of raspberry fruits and changes
during processing
In contrast with results obtained when analysing anthocyanin composition, only quantitative di†erences were
found between both raspberry varieties when Ñavonol
composition was studied. Quercetin 3-glucoside plus 3glucuronide (co-eluting under our conditions) and
kaempferol 3-glucoside and 3-glucuronide (also coeluting) were detected (Table 7), in accordance with previous Ðndings in red raspberry juice (Rommel and
Wrolstad, 1993). It is also remarkable that quercetin 3glycoside presents a high stability during processing as
570
C Garc• a-V iguera et al
TABLE 3
Anthocyanins stability of red raspberry jam elaborated with frozen fruit (cv Zeva) during storage
at 20, 30 and 37¡Ca
Cy 3-soph
Cy 3-glc-rut
Cy 3-glc
Cy 3-rut
Initial
182É58 (^18É30)
57É56 (^7É59)
504É54 (^63É39)
235É85 (^36É85)
Days at 20¡C
32
62
95
108
123
139
159
179
188
129É81
77É53
32É71
27É35
16É64
16É47
13É73
15É64
13É47
(^12É71)
(^7É35)
(^0É80)
(^2É69)
(^0É71)
(^1É42)
(^1É69)
(^0É64)
(^3É98)
47É46
30É80
8É82
8É09
7É47
7É31
6É31
6É13
3É62
(^3É47)
(^2É36)
(^0É04)
(^0É69)
(^0É11)
(^0É51)
(^0É80)
(^0É42)
(^0É02)
328É77
173É16
74É81
58É57
33É06
30É33
23É93
24É22
24É46
(^35É66)
(^17É66)
(^3É18)
(^8É11)
(^1É53)
(^2É22)
(^2É87)
(^1É47)
(^1É02)
163É56
89É12
36É49
22É62
19É09
17É35
13É58
12É53
12É15
(^14É44)
(^7É75)
(^1É12)
(^4É71)
(^0É76)
(^1É82)
(^1É69)
(^0É84)
(^0É60)
Days at 30¡C
32
62
95
108
123
139
72É17
28É75
5É40
4É49
2É69
1É67
(^9É78)
(^4É38)
(^0É51)
(^0É49)
(^1É33)
(^0É36)
28É29
13É89
2É98
2É87
1É38
0É82
(^3É22)
(^1É98)
(^0É49)
(^0É20)
(^0É69)
(^0É16)
157É16
48É75
8É27
7É31
4É22
2É42
(^18É02)
(^7É27)
(^1É44)
(^0É49)
(^2É04)
(^0É38)
83É35
30É60
5É29
4É89
2É47
1É47
(^7É60)
(^4É67)
(^0É13)
(^0É62)
(^1É29)
(^0É22)
Days at 37¡C
32
62
23É18 (^1É47)
4É82 (^1É00)
11É02 (^0É76)
2É64 (^0É64)
40É93 (^2É91)
7É31 (^0É84)
25É04 (^2É58)
5É75 (^1É47)
a Values are expressed as in Table 2.
TABLE 4
Anthocyanins stability of red raspberry jam elaborated with
fresh fruit (cv Heritage) during storage at 20, 30 and 37¡Ca
Cy 3-soph
Cy 3-glc
Initial
518É78 (^61É76)
364É17 (^43É56)
Days at 20¡C
31
53
88
106
120
139
155
175
191
308É70
125É48
77É77
74É84
65É28
60É04
39É82
36É82
28É22
(^56É51)
(^15É22)
(^15É20)
(^4É29)
(^8É89)
(^5É56)
(^7É04)
(^6É09)
(^3É42)
182É38
70É64
42É48
33É40
32É02
27É75
11É75
10É84
10É29
(^33É51)
(^8É80)
(^8É20)
(^3É58)
(^11É71)
(^2É51)
(^1É60)
(^0É33)
(^0É60)
Days at 30¡C
31
53
88
106
120
139
189É07
43É62
17É11
16É58
15É27
11É84
(^47É80)
(^4É29)
(^1É36)
(^0É09)
(^2É62)
(^0É20)
96É63
18É49
6É15
5É82
4É73
4É16
(^24É73)
(^2É29)
(^0É62)
(^0É11)
(^0É69)
(^0É16)
Days at 37¡C
31
53
105É94 (^12É69)
6É20 (^1É04)
the content of this Ñavonoid per gram of fruit was
reduced only on a ^ 6% for both varieties, while when
kaempferol 3-glycoside is considered the content is
reduced on a ^22% (Table 7).
DISCUSSION
a Values are expressed as in Table 2.
49É80 (^4É53)
1É51 (^0É47)
The results obtained with jams stored at di†erent temperatures are in accordance with previous reports on
other food products (Spayd and Morris 1981 ; Withy et
al 1993). Thus, the stability of anthocyanins and the rate
of their degradation is markedly inÑuenced by temperature, and formation of chalcone form is favoured by
increasing temperature, during storage and processing,
at the expense of the other species (Markakis 1982 ;
Jackman and Smith 1996). It has also been demonstrated that the concentration of polymeric pigments
increase with temperature and storage time, and this
has an important inÑuence in the colouration of juices
and red wines (Somers 1971 ; Adams and Ongley 1973 ;
Bakker and Timberlake 1986 ; Withy et al 1993). In this
aspect it is remarkable that the rate of colour loss is
much slower than the rate of anthocyanin degradation
(Figs 1 and 2).
Although the expression of anthocyanin colour is well
known to be pH dependent (Brouillard 1982) these jams
571
Colour and anthocyanin stability of red raspberry jam
TABLE 5
Anthocyanins stability of red raspberry jam elaborated with
frozen fruit (cv Heritage) during storage at 20, 30 and 37¡Ca
Initial
Cy 3-soph
Cy 3-glc
399É56 (^42É22)
274É97 (^24É24)
Days at 20¡C
31
53
88
106
120
139
155
175
191
292É88
106É10
52É51
48É82
47É22
45É46
25É75
24É62
21É82
(^19É06)
(^3É36)
(^3É84)
(^9É67)
(^3É31)
(^1É22)
(^1É31)
(^0É89)
(^4É64)
167É89
57É75
24É71
22É60
20É89
20É49
9É00
7É84
7É09
(^6É75)
(^2É20)
(^1É31)
(^4É27)
(^0É31)
(^1É22)
(^0É60)
(^1É82)
(^0É31)
Days at 30¡C
31
53
88
106
120
139
136É28
43É57
10É02
8É67
8É44
3É73
(^26É35)
(^0É27)
(^0É04)
(^0É20)
(^0É91)
(^0É76)
69É06
15É20
2É87
2É47
2É60
1É38
(^10É87)
(^0É20)
(^0É01)
(^0É47)
(^0É44)
(^0É62)
Days at 37¡C
31
53
74É79 (^14É09)
9É22 (^2É64)
31É82 (^6É89)
2É82 (^1É64)
a Values are expressed as in Table 2.
TABLE 7
Flavonol losses during red raspberry jam manufacturing
(mean ^ SD, n\3)a
Quer 3-gly
Fruit
Jam
Kaemp 3-gly
Fruit
Jam
Frozen fruit
(cv Zeva)
Frozen fruit
(cv Heritage)
33É79 (^2É27)
31É79 (^2É51)
52É65 (^3É17)
50É02 (^4É23)
7É14 (^0É68)
5É73 (^0É90)
7É17 (^0É69)
5É74 (^0É88)
a Values are micrograms of Ñavonoids per gram of fruit in jam
(fresh weight). HPLC reproducibility was ca ^6%. Quer
3-gly, Quercetin 3-glycoside ; Kaemp 3-gly, Kaempferol 3glycoside.
fell within a narrow pH range from 3É22 to 3É46, averaging 3É33, and thus, pH was not a signiÐcant factor in
colour expression in these jams. Therefore, other factors
may have a signiÐcant role in the expression of colour
in raspberry jams by co-pigmentation or some other
physicochemical processes. In addition to anthocyanin,
it has been reported that red raspberries also contain
high concentrations of phenolic acids (Schwab and
Herrmann 1985), Ñavonols (Henning 1981) and Ñavan3-ols (Mossel and Herrmann 1974), which are known to
TABLE 6
L *a*b and Hue angle values obtained for red raspberry jams prepared with fresh or
frozen fruit
Zeva fresh
Zeva frozen
Heritage fresh
Heritage frozen
L*
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
32É73
34É69
34É27
30É92
(^0É94)
(^1É70)
(^0É42)
(^0É43)
33É78
36É01
34É54
30É82
(^0É24)
(^1É68)
(^0É27)
(^0É32)
36É30
41É69
40É74
35É04
(^0É27)
(^1É64)
(^0É30)
(^1É22)
37É36
43É20
40É88
38É25
(^0É09)
(^1É28)
(^0É17)
(^0É53)
a*
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
31É63
18É53
23É48
24É28
(^2É03)
(^1É52)
(^0É60)
(^1É56)
33É04
19É42
22É50
23É25
(^0É31)
(^1É30)
(^0É97)
(^0É92)
36É65
17É32
25É01
30É46
(^0É42)
(^0É62)
(^0É17)
(^2É22)
37É42
16É75
21É15
29É89
(^0É52)
(^0É47)
(^0É30)
(^0É33)
b*
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
13É79
15É24
13É60
9É85
(^1É50)
(^2É36)
(^0É51)
(^0É68)
15É10
16É35
14É11
9É78
(^0É34)
(^0É47)
(^0É30)
(^0É61)
18É29
22É74
18É47
14É78
(^0É23)
(^1É24)
(^0É35)
(^1É07)
19É16
24É69
20É29
17É34
(^0É40)
(^1É70)
(^0É39)
(^0É34)
H
Initial
108 (37¡C)
139 (30¡C)
207 (20¡C)
23É55
39É53
30É08
22É07
(^0É64)
(^1É00)
(^0É70)
(^0É41)
24É56
40É09
32É09
22É82
(^0É83)
(^0É35)
(^0É30)
(^0É59)
26É52
52É71
36É44
25É88
(^0É50)
(^1É11)
(^1É12)
(^0É45)
27É12
55É84
43É81
30É12
(^0É66)
(^1É30)
(^0É92)
(^0É88)
Data obtained initially (day 0) and at the end of the experiment, at the di†erent temperatures (day 108 at 37¡C, day 139 at 30¡C and day 207 at 20¡C). Standard Deviation in
brackets.
572
C Garc• a-V iguera et al
interact with anthocyanins to produce an increase in
colour intensity and a bathocromic shift in the spectrum
of the anthocyanin to give purple to blue colours
(Francis 1975 ; Mazza and Brouillard 1990 ; Garc• aViguera et al 1994 ; Rivas-Gonzalo et al 1995). All previous studies have been done in liquid solutions (juices,
wines or model system). Nevertheless, it may be
assumed that the same reactions take place in jams even
if the bathocromic shift is not as evident as in liquid
media and no precipitation is shown, due to the formation of polymers.
Zeva cultivar presented a higher monomericanthocyanin amount but “HeritageÏ a* value was higher
during the experiment, conÐrming that the monomeric
species are not the main factor in colour expression.
This may be explained, partially, if the concentration of
Ñavonols is considered, as colour is the result of the
physical interaction of electrons between the anthocyanin and co-pigments rings within the anthocyanin/
co-pigment complex, and Ñavonols have proved to be
the most efficient co-pigments (Mazza and Miniati
1993). When the Ñavonol composition of both varieties
was analysed quercetin and kaempferol 3-glycosides
(glucoside plus glucoronide co-eluting) were found
(Table 7). Nevertheless, “ZevaÏ presented a lower concentration, of quercetin 3-glycoside (33É79 lg g~1 fresh
fruit), than “HeritageÏ (52É65 lg g~1), while both varieties contained similar amounts of kaempferol 3glycoside (7É14 lg g~1 and 7É17 lg g~1, respectively).
Moreover, during processing only ^ 6% of quercetin
3-glycoside was lost (Table 7) ; therefore, a considerable
amount of this Ñavonol is present in the jams. Quercetin
derivatives are well known co-pigments (Mazza and
Miniati 1993). Thus, the di†erences found in this copigment concentration could explain the higher red hue
found for “HeritageÏ at the beginning of the assay, but
not at the end of each experiment, when total anthocyanin concentration had decreased to less than ^ 10%
of the initial value. Therefore, the di†erences found in
colour, during storage, are more likely to be due to polymerisation phenomena, similar to what was mentioned
above for wines or juices.
It can also be concluded that the colour of processed
and stored at 20¡C products is not signiÐcantly a†ected
by freezing for 24 h. Moreover, although total anthocyanin concentration is lower when jam was made with
frozen fruit, the rate of loss of these compounds during
storage was not inÑuenced by this factor. Nevertheless,
the development of browning was higher when jams
were produced with frozen fruit and stored at higher
temperatures.
ACKNOWLEDGEMENTS
CGV wish to thank the Spanish Ministerio de Educacion y Ciencia, via CSIC, for a contract and PZ to Hero
Espan8 a SA for a grant. Thanks also to C Mart• nez Ataz
for technical assistance.
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