Development of continuous microwave pasteurization system for liquid foods
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Date
2017
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DIVISION OF FOOD SCIENCE & POSTHARVEST TECHNOLOGY ICAR - INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI –
Abstract
A continuous pasteurization system for liquid foods was developed. The developed
system used microwave power to heat the liquid food instead of conventional
heating.
Preliminary experimentation to obtain a time-temperature combination for complete
inactivation of B. cereus and S. cerevisiae using nutrient and MGYP broths
respectively was undertaken using conventional heating method.
The developed system was subsequently tested for its efficacy in reducing microbial
load (B. cereus and S. cerevisiae) in model liquid system at 90 and 60°C
respectively. It was found that microwave heating could completely eliminate the
microbial load in each of the two liquid systems in significantly lower residence
times (3 min. instead of 8 min. for B. cereus and 5 min. instead of 7 min. for S.
cerevisiae) compared to those using conventional heating. The developed continuous
microwave pasteurization system tested for pasteurization of sugarcane juice and soy
milk using different combinations of microwave power levels (210, 280, 350, 420 &
490 Watts) for heating the liquids to 70°C and 100°C respectively. The heated
liquids were then held for 10 min. and 1 min. respectively at 70° and 100°C, cooled,
qualitative evaluation done and storability studied under refrigerated condition
(4±1°C).
Quality evaluation of the Pasteurized sugarcane juice and soy milk showing
maximum retention of total antioxidant content was subsequently stored under
refrigerated conditions (4±1ºC) in transparent glass bottles.
Colour (L*, a*, b*) values of fresh sugarcane juice added with citric acid, thermal
pasteurized and microwave pasteurized juices were significantly higher from that of
fresh sugarcane juice. There was no significant difference in TSS and pH values of
any of the pasteurized sugarcane juice. PPO activity and total viable bacterial count
decreased significantly after thermal and microwave pasteurization of juice whereas
yeast was completely eliminated from all the microwave pasteurized and thermal
pasteurized sugarcane juices. There was a significant decrease in total antioxidant
values after thermal and microwave pasteurization whereas sensory scores of fresh
sugarcane juice added with citric acid did not change significantly after thermal and
microwave pasteurization.
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There was no significant difference in colour (L*, a*, b*), T.S.S. and pH values
between the fresh, thermal pasteurized and microwave pasteurized soy milk. Total
antioxidants, total phenols, LOX activity and total viable bacterial count in freshly
prepared soy milk decreased significantly after thermal and microwave
pasteurization. There was no significant difference in Colour and texture of Soy milk
after microwave and thermal pasteurization whereas beany flavour, taste and overall
acceptability scores changed significantly after microwave and thermal
pasteurization.
During storage there was no significant difference in colour (L*, a*, b*) and TSS
values of microwave pasteurized sugarcane juice at 490 Watt and thermal
pasteurized (control) sugarcane juice throughout the storage period.There was a
significant decrease in pH, residual PPO activity and total antioxidant content in
microwave pasteurized and thermal pasteurized sugarcane juice with the increase in
storage period.There was a significant increase in total viable bacterial count in
microwave pasteurized and thermal pasteurized sugarcane juice at the end of storage
whereassensory scores of microwave pasteurized and thermal pasteurized sugarcane
juice decreased gradually during storage.
During storage there was no significant difference in colour (L*, a*, b*) values of
microwave pasteurized soy milk at 420 watt throughout the storage period where as
colour (L*, a*, b*) values for thermal pasteurized (control) soy milk changed
significantly at the end of storage. There was no significant difference in TSS values
of microwave pasteurized and thermal pasteurized soy milk throughout the storage
period. There was a decrease in pH, residual LOX activity, total antioxidants and
total phenols content in microwave pasteurized and thermal pasteurized soy milk
with the increase in storage period. There was a significant increase in total viable
bacterial count in microwave pasteurized and thermal pasteurized soy milk at the end
of storage whereassensory scores of microwave pasteurized and thermal pasteurized
soy milk decreased gradually during storage.
Microwave technology can be used successfully for the pasteurization of liquid foods
with higher retention of nutritional and functional quality of liquid foods.
Description
t9614
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