CONTROL (shelf-stable milk)

CONTROL (shelf-stable milk)

Summary

Significant hazards a r Cl. botulinum and toxigenic bacilli.

Control measures

Initial level (H 0 ) r Low levels of pathogens in raw milk are likely (see section on raw milk). Use milk from healthy animals, milked according to good milking

practices; cool milk during intermediate storage on the farm and during transportation to dairy plants (≤6 ◦

C recommended). Reduction (ΣR)

r Heat treatments applied are sufficient to destroy vegetative microorganisms and to reduce Cl. botulinum by approx. 12 log 10 units.

r Process milk according to HACCP principles with special attention to

the control of heating and aseptic filling. r Cleaning and disinfection after processing are essential.

Increase (ΣI) r Post-process contamination may occur during aseptic filling and packing and during distribution if packaging materials damaged.

r Growth of contaminating microorganisms during storage and

distribution.

Testing

r Routine testing for pathogens is not recommended. r Incubation tests to detect deviations from Good Hygienic Practice. In

cases of sensitive products (e.g. baby foods), 100% can be tested by non-destructive methods (e.g. vacuum test).

Spoilage

r Spoilage may occur due to the growth of contaminating microorganisms. Parameters are off-taste, off-odor, curdling/coagulation.

a In particular circumstances, other hazards may need to be considered.

Hazards to be considered Heating technology is applied so that microbial hazards arising from raw milk are controlled. Prob-

lems arising from contaminated raw milk indicate inappropriate heating technology. Recontamination may occur during filling the heated product into containers such as bottles and cartons.

Control measures Initial level of hazard (H 0 ). Initial level of the processed milk will depend on the previous processing

steps, starting with the raw milk up to the UHT treatment. Reduction of hazard (ΣR). Sterilization processes may be characterized by the number of decimal

reductions of viable spores achieved during processing. As time-temperature parameters for UHT purposes are almost constant and defined, the initial spore load is critical relative to the potential for survivors. Spore loads in raw milk may fluctuate according to the season (Phillips and Griffiths, 1986). The type of spores, and hence their resistance to heating, can also vary depending on the origin of raw materials, e.g. milk, cocoa powder, malt extract, or carrageenan. This should be taken into account when developing new products or when modifying existing recipes. Consequently, modification of process

667 Cleanliness and sterility of all equipment that will come into contact with milk is a prerequisite to

MILK AND DAIRY PRODUCTS

starting production. Heat exchangers should be carefully monitored during maintenance and disman- tling. Defective heat exchangers may be a source of cross-contamination. Cooling water, or other cooling fluids, may be a source of contamination, including when cans are cooled, and should be disinfected.

Increase of hazard (ΣI). Design and maintenance of the process equipment is of utmost importance and material should be chosen carefully. Particular attention should be paid to aspects such as connections of pipes, presence of bends or dead ends, cleanability of valves, pumps, etc. These technical aspects are important to guarantee efficient cleaning, in particular cleaning in place (CIP) where physicochemical parameters such as flow rates, temperature of fluids, and concentration of chemicals can be critical to effective cleaning.

The fillers can be considered as “open and unprotected parts” of UHT-lines. Installation in locations separate from processing areas help minimize the risk of contamination. Sterile airlocks, steam seals, and other protection permit their installation in processing areas. Good environmental hygiene to avoid build-up of contaminants in this zone, quality of air, and hygiene of operators are further important aspects of product protection.

Packaging material can be classified as a raw material and its microbiological quality depends on its manufacturing process (Reuter, 1987). Further contamination by dust particles carrying microorganisms should be avoided during transport, handling, and storage. Sterilization of packaging is important and should be carefully controlled. An efficient treatment is possible only if the key parameters of each treatment such as time, temperature, dose, or concentration or sterilant are carefully monitored and any deviations corrected.

When milk is UHT-treated and then filled into bottles under non-aseptic conditions prior to final in-bottle sterilization, filling can be done at 50-70 ◦

C. In such processes, sporulation of thermophilic bacilli may occur in the filler and spores will not be inactivated in the subsequent sterilization. Cleaning and disinfection every 6-8 h is needed to limit build-up of Bacillus spp. and avoid the onset of the sporulation cycle.

Testing Incubation tests alone are not sufficient to guarantee the quality and safety of a product and should

be integrated into a preventive system based on HACCP (ICMSF, 1988; Cordier, 1990). Checking the final products is not feasible, for technical and practical reasons, and even analysis of large numbers of samples would not assure complete safety. Analysis of 100% of the manufactured units is normally only performed during the commissioning of new equipment or the start-up of new lines. As experience increases, however, sampling frequency is gradually reduced to for example 0.1% or less or to a fixed number of units per lot. For this verification, routine samples withdrawn at regular intervals and event samples taken after start or end of production, after a line stops, roll, or strip changes, etc. are analyzed.

Quality and safety of the final product depends on adequate sealing and complete integrity of seals. Visual inspection is an effective means of monitoring. Maintenance of this integrity throughout distri- bution from the manufacturer to the consumer is essential.

Spoilage Spoilage is characterized by the development of off-tastes and off-odors and physical changes of the

product (curdling or coagulation) similar to the one observed for pasteurized products. Incubation tests for five days at 30 ◦

C should result in total counts of ≤ 10 per 0.1 mL after incubation of the agar plates for

72 h at 37 ◦

C. This test is also applicable when checking for B. sporothermodurans. Incubation tests of a

MICROORGANISMS IN FOODS 6

of the process. Microbiological tests performed after incubation allow spoilage microorganisms to be identified and provide useful information for trouble shooting. Indicator tests include the total count of mesophilic bacteria.