Trials were further conducted for power of 100 W and it was
observed that at ultrasonic power of 100 W and treatment time
of 15 min, around 4 log reduction was achieved in a juice sample
volume of 250 ml. Enhanced sensory and nutrient attributes were
also exhibited by juice samples that were treated at higher power
levels (100 W) as compared to the ones treated at lower power
levels. This may be attributed to the fact that ultrasound along with the bactericidal action also contributes towards extraction of
flavor and odor components which resulted in sensory enrichment
of the juice. At higher levels of ultrasonic power, cavitational
effects are intensified [30], which lead to enhanced disintegration
of fruit flesh cells and a higher rate of mass transfer leading to
higher release of the active ingredients [31,32]. Many researchers
have also demonstrated that a higher ultrasonic power resulted
in the enhancement of extraction efficiency of sugars [33],
organic acids [34] and phenolic compounds [35]. Due to the
mechanical action of ultrasound, the solute particles diffuse
easily in the water because of the greater contact between the
solute and the solvent [36]. It was also observed that extended
treatment using ultrasonic power of above 100 W power and treatment time beyond 15 min, reduced the ascorbic acid and phenolic
content with slight decline in the sensory attributes. The observed
trends can be attributed to the fact that the quality and sensory
attributes are based on the highly sensitive compounds, which
get affected negatively when exposed to harsh environment of cavitating conditions over extended durations. Based on these results,
it can be established that higher ultrasound energy input till an
optimum is necessary to definitely damage the microbial cell walls
to the required extent. Also the treatment of juices by ultrasound
at operating power of 100 W improved the nutritional quality of
the processed juice. Considering these results, an optimum ultrasonic power of 100 W and treatment time of 15 min was used in
all the remaining sets of experiments. Experiments were also conducted to investigate the effect of duty cycle over the range of 20–
80% and it was established that a duty cycle of 50% as optimum
resulted in adequate results satisfying all prerequisites of ultrasound induced pasteurization technique. The simultaneous sterilization experiments using ultrasound and UV were conducted in
the same manner as the earlier experiments conducted using only
ultrasound and with optimized ultrasound parameters. It was
observed that the exposure to UV light simultaneously during
the 15 min of sonication treatment resulted in more than 5 log
reduction of food borne pathogens.
Trials were further conducted for power of 100 W and it wasobserved that at ultrasonic power of 100 W and treatment timeof 15 min, around 4 log reduction was achieved in a juice samplevolume of 250 ml. Enhanced sensory and nutrient attributes werealso exhibited by juice samples that were treated at higher powerlevels (100 W) as compared to the ones treated at lower powerlevels. This may be attributed to the fact that ultrasound along with the bactericidal action also contributes towards extraction offlavor and odor components which resulted in sensory enrichmentof the juice. At higher levels of ultrasonic power, cavitationaleffects are intensified [30], which lead to enhanced disintegrationof fruit flesh cells and a higher rate of mass transfer leading tohigher release of the active ingredients [31,32]. Many researchershave also demonstrated that a higher ultrasonic power resultedin the enhancement of extraction efficiency of sugars [33],organic acids [34] and phenolic compounds [35]. Due to themechanical action of ultrasound, the solute particles diffuseeasily in the water because of the greater contact between thesolute and the solvent [36]. It was also observed that extendedtreatment using ultrasonic power of above 100 W power and treatment time beyond 15 min, reduced the ascorbic acid and phenoliccontent with slight decline in the sensory attributes. The observedtrends can be attributed to the fact that the quality and sensoryattributes are based on the highly sensitive compounds, whichget affected negatively when exposed to harsh environment of cavitating conditions over extended durations. Based on these results,it can be established that higher ultrasound energy input till anoptimum is necessary to definitely damage the microbial cell wallsto the required extent. Also the treatment of juices by ultrasoundat operating power of 100 W improved the nutritional quality ofthe processed juice. Considering these results, an optimum ultrasonic power of 100 W and treatment time of 15 min was used inall the remaining sets of experiments. Experiments were also conducted to investigate the effect of duty cycle over the range of 20–80% and it was established that a duty cycle of 50% as optimumresulted in adequate results satisfying all prerequisites of ultrasound induced pasteurization technique. The simultaneous sterilization experiments using ultrasound and UV were conducted inthe same manner as the earlier experiments conducted using onlyultrasound and with optimized ultrasound parameters. It wasobserved that the exposure to UV light simultaneously duringthe 15 min of sonication treatment resulted in more than 5 logreduction of food borne pathogens.
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