Microbial content TPC Result and Discussion

Proceeding of 2013 International Seminar on Climate Change and Food Security ISCCFS 2013 Palembang, South Sumatra -Indonesia, 24-25 October,2013 165

3.2.2. Internal temperature

Pepes internal temperature was measured using a thermometer insertion at four points, namely in abdomen belly, near the head anterior, in the middle of the body middle and near the tail. Average internal temperature were expressed in Celcius degrees °C. A safe minimum internal temperature for fish is 145°F or 63 °C [15] .

3.2.3. Visual observation

Visual observation of well done state of pepes was conducted by using Suwandi 1990 method [2] with a slight modification, namely additional characteristics of fish, including fat color and texture of spices.

4. Result and Discussion

4.1. Microbial content TPC

In general, microbial content of pepes measured as total plate count TPC showed that the populations were under standard maximum limits, namely 5x10 5 CFUg or 5.70 log CFUg. Increasing cooking time led to a decrease in the number of microbial colonies. The average value of TPC was 4.89 log CFUg for A 1 treatment: cooking for 4 minutes, 4.77 log CFUg for A 2 treatment: cooking for 5 minutes and 4.75 log CFUg for A 3 treatment: cooking for 6 minutes Figure 1. Fig. 1: The average values of total plate count TPC of pepes heated with microwave oven The results were in accordance with those of Hollywood, Varabioff and Mitchell 1991 [19] who studied the effect of microwave cooking and conventional oven on temperature profiles and microbial flora of beef. Mesophilic microbial colony counts contained in beef studies showed a decrease with increasing time after the cooking and standing. The conclusion of that study was food cooking by microwave need adequate procedure and standing time after the food was cooked in order to achieve the balance of temperature and exposure to microbes. The destruction of microorganisms during microwave heating was mainly caused by the heat generated by microwaves [20] . Heat caused denaturation of proteins that destroy the activity of the enzyme which controls the metabolism of microorganisms [21] . TPC data of pepes were then used to determine D value with reference to Winarno 1994 [22] . Linear equation obtained from the relationships of heating time of microwave oven and the number of survived microbes in pepes was shown on Figure 2. D value was then calculated from the resulting equation of y = - 0.070 x + 5.156 and gave 14.28 minutes. The following conditions of microwave oven were applied: power 800 W and frequency 2450 MHz. In other words, killing of 90 of the microbial population in pepes could be accomplished in 14.28 minutes. Jeng et al. 1987 showed that the sporicidal mechanism of microwave was caused by thermal effects [23] . That study showed that D value on sterilization of dried spores of Bacillus subtilis subsp. niger are 88, 14 and 7 minutes at 117, 130 and 137 °C, respectively. Proceeding of 2013 International Seminar on Climate Change and Food Security ISCCFS 2013 Palembang, South Sumatra -Indonesia, 24-25 October,2013 166 Fig. 2: Effects of microwave oven heating time on the number of microbes in pepes

4.2. Internal temperature