ABSTRACT
Prevention of physical instability of chocolate milk is an important challenge in the field of food science, particularly dairy technolohy. In this study, the effects of high-intensity ultrasound treatment on stability of cocoa particles in chocolate milk, with or without the presence of stabilizers, was investigated. Chocolate milk was exposed to ultrasound [maximal nominal power 600 W at 20 kHz] at various levels of power intensity [24, 72 and 120 W], exposure times [2, 6 and 10 minutes] and temperatures [25, 45 and 65°C] for 30 days. k-carrageenan at concentrations of 0.000, 0.010, 0.015 and 0.020%, with or without sugar [7.0% and 0.0%], was added to the samples. Increasing power intensity and exposure time led to a significant increase in physical stability of the milk samples - the milk phase volume decreased and the cacao phase increased. Moreover, the phase separation and cacao particle sedimentation were effectively prevented in the treated samples [ultrasonic power 120W, exposure time 2 min, temperature 45°C, k-carrageenan 0.02%, and sugar 7%] after 30 days of storage at 4°C, while phase separation and cacao particle sedimentation occurred in the control sample [containing 0.040% k-carrageenan]. The findings also showed that sugar improved cacao milk stability. The milk phase volume in the presence of 0.02% k-carrageenan, kept at a temperature of 45°C for 30 days, was less than that of samples kept at other temperatures. Based on the findings of the present study, it seems that ultrasound can increase the stability of cacao particles in milk. In addition, ultrasound treatment possibly degrades the k-carrageenan network, particularly at higher temperatures. Furthermore, cavitation, probably due to entrapment of air in the k-carrageenan network, may weaken the gel network
ABSTRACT
Raw milk is a source of new strains of bacteriocin-producing lactic acid bacteria [LAB] with the potential to inhibit undesirable microorganisms. The aim of this work was to detect the bacteriocin-producing LAB from raw ewe's and goat's milks and characterize the isolated bacteriocins. A total of 100 samples of ewe's and goat's milks were screened for bacteriocin-producing lactic acid bacteria. Two strains were selected and identified phenotypically to genus level. The serums of cultures of the selected strains were treated with various enzymes to detrmine the nature of their antimicrobial substances. The inhibition potential of the substances was investigated by agar well diffusion assay and their stability at different temperatures and pH's were determined. The antimicrobial substances were partially purified by ammonium sulphate and poly-ethylene gltcol [PEG] and the titer determined. In addition, their molcular weights were determined by SDS-PAGE analysis and their resistance estimated during storage at 4°C. The two strains of Enterococcus, Le40 and Le50, exhibited a broad antimicrobial activity in several replicates. The sensivity of the inhibitory substances to proteolytic enzymes confirmed the production of enterocin-like substances [ELS] by these strains. Listeria monocytogenes and Staphylococcus aureus were inhibited by the ELSs. The ELSs were both stable at a wide pH range [pH 3-10] and the one isolated from Le50 was resistant to heat. Partial purification of both the ELSs increased their activity and titer. Their molcular weights were between 24 and 29 KD. Finally, the ELS's activity was maintained during storage at 4°C for 28 days. Considering the desirable antimicrobial characteristics and biochemical properties of the isolated ELSs, further studies to explore the possibility of using them as biopreservatives in food processing is recommended
ABSTRACT
In the last few years there has been a growing trend to use chickpea as a good protein source. Chickpea protein products, such as chickpea flour, concentrate and isolate, are considered as functional food supplements, alternatives to soy protein. The objective of this study was to determine and compare the functional and thermal properties of chickpea and soy-protein concentrates and isolates. Chickpea protein concentrate and isolate were prepared from defatted chickpea flour by applying alkaline extraction and isoelectric precipitation. Chemical composition [protein, fat, ash, crude fiber, and water contents], functional properties [water and fat absorptions, gelation, foaming capacity, and foam stability], and thermal properties [glass transition and denaturation temperatures] of chickpea protein concentrate and isolate were determined and compared with those of the soy protein products. The protein contents of the concentrate and isolate obtained from defatted chickpea flour were 80% and 88.6%, respectively; the corresponding proportions for soy concentrate and isolate were 83.1% and 90.2%. There were no statistically significant differences as regards water and oil absorptions between soy and chickpea proteins. The gelation properties and foaming capacity of all the samples increased with an increase in protein concentration. However, soy protein had a higher foaming capacity and foam stability as compared to chickpea protein [P
ABSTRACT
The use of edible coatings is a suitable method to reduce oil uptake in fried foods. In this research, the effects of soy-protein isolate [SPI] coating plasticized with sorbitol on oil uptake reduction and sensory and physical properties of deep-fat fried French fries were investigated. Potato strips were coated with SPI plasticized with sorbitol at different concentrations. The effect of coating on oilp uptake reduction, water retention, crispiness and color change of French fries were determined, using response surface methodology. Moreover, the sensory acceptability of the tried potato samples was assessed. The results showed that the protein and sorbitol concentrations are the major factors affecting water retention, oil uptake reduction, crispiness, and color of the fried potato samples. Coating resulted in oil uptake reduction and water retention up to 40% +/- 2 and 80%, respectively. Nonsignificant differences in sensory characteristics of coated and uncoated samples were observed. The results showed that the models based on the response surface methodology are quite suitable for the evaluation of the effects of coating on the properties of french fries. The application of soy-protein coating reduces oil uptake, while it does not affect the sensory characteristics, of fried potato strips. It is concluded, then, that SPI coating can improve the organoleptic and nutritional properties of fried food products
ABSTRACT
Recently, especial therapeutic effects and nutritional values of probiotic dairy products have made them as one of the most interesting research topics in the field of production and maitenance methods and the nutritional and therapeutic aspects of these products. The technological problems encountered in the production of these products can be overcome by using methods to improve the growth of probiotic bacteria in fermented milk. In this paper the effect of milk composition [skim milk and whey powder], percent of inoculum [Lactobacillus acidophilus La-5 and starter culture] and incubation temperature on the growth of the probiotic bacteria in yogurt was investigated, and suitable conditions to reach maximum growth were determined using the Taguchi design. The effect of five independent variables [at three levels] on the growth of Lactobacillus acidophilus La-5 [6 hr incubation] in probiotic yogurt production was investigated by Taguchi approach. The variables included: skim milk powder [10, 12, 14% w/w], whey powder [0, 0.75, 1.5% w/w], size of yogurt culture inoculum [0.2, 0.4, 0.8% v/v], L. acidophilus inoculum [0.1, 0.3, 0.5% w/v], and incubation temperature [37, 40, and 43°C]. Among the variables evaluated, yogurt culture inoculum had the maximum effect on the growth of probiotic bacterium, while the incorporation of L. acidophilus inoculum and the incubation temperature had no significant effect on the bacterial growth stimulation. Anyway the most suitable conditions for enhancing the probiotic bacterial growth include: skim milk powder, 10% w/w; without adding whey powder and size of yogurt culture and L. acidophilus inoculum, 0.1%w/v and 0.4% v/v, respectively incubation temperature at 37°C. By exact determination of milk composition, inoculum size and incubation temperature, the maximum number of the probiotic bacterium can be achived in the product. Data of this research work, that are very useful for the industrial production lines, show that by using the minimum level of milk total solid, without the enrichment and by adding the standard yogurt inoculum size and minimum probiotic inoculum size and by low incubation temperature, the growth rate increased and the production of probiotic yogurt with high number of Lactobacillus acidophilus become possible