Effect of Different Molecular Weight Hyaluronic Acids on Skim Milk Functional Properties.

Hyaluronic acid (HA), a naturally occurring polysaccharide with recognized health benefits, has gained approval for use in the food industry as a food additive, ingredient, and health supplement in numerous countries. HA can increase viscosity in solutions and is available commercially in various molecular weights (MW) depending on end applications. Nevertheless, no research has explored the impact of different MW HAs on functionality, rheological properties, and texture-building benefits in the dairy product matrix wherein they are incorporated. Therefore, the objective of this study was to evaluate how varying MWs of HA-specifically 8 kDa, 320 kDa, 980 kDa, and 2550 kDa at 0.25% (w/w) concentration-impact rheological characteristics, functional attributes, heat stability, protein stability, protein structure, and protein fractions within skim milk. The addition of HA led to an increase in the apparent viscosity of all samples. A higher G″ value over G' values for all HA samples was observed in frequency sweep, indicating the absence of interparticle interactions between HA particles. Protein stability and heat stability were significantly lower for 980 kDa and 2550 kDa HA as compared to the control and 8 kDa HA samples. As the MW increased, WHC, emulsion properties, and foaming stability notably increased. However, reversed results were found in the case of foaming activity. Moreover, no significant changes were observed in the percent area of individual protein fractions and the hydrodynamic diameter of protein particles. This study would help to understand the effect of HA when incorporated in dairy products for water binding or enhancement in viscosity-based applications.

Effect of Hyaluronic Acid and Kappa-Carrageenan on Milk Properties: Rheology, Protein Stability, Foaming, Water-Holding, and Emulsification Properties.

Hyaluronic acid (HA) is now widely known for its ability to bind water and impart texture. The combined effects of HA and kappa-carrageenan (KC) have not yet been investigated, though. In this study, we looked at the synergistic effects of HA and KC (concentrations of 0.1 and 0.25%, and ratios of 85:15, 70:30, and 50:50 for each concentration) on the rheological properties, heat stability, protein phase separation, water-holding capacity, emulsification properties, and foaming properties of skim milk. When HA and KC were combined in various ratios with a skim milk sample, this resulted in lesser protein phase separation and a higher water-holding capacity than when HA and KC were utilized separately. Similarly, for the sample with a 0.1% concentration, the combination of HA + KC blends demonstrated a synergistic impact with greater emulsifying activity and stability. The samples with a concentration of 0.25% did not exhibit this synergistic effect, and the emulsifying activity and stability were mostly due to the HA's higher emulsifying activity and stability at 0.25% concentration. Similarly, for rheological (apparent viscosity, consistency coefficient K, and flow behavior index n) and foaming properties, the synergistic effect of the HA + KC blend was not readily apparent; rather, these values were mostly due to an increase in the amount of KC in the HA + KC blend ratios. When HC-control and KC-control samples were compared to various HA + KC mix ratios, there was no discernible difference in the heat stability. With the added benefits of protein stability (reduced phase separation), increased water-holding capacity, improved emulsification capabilities, and foaming abilities, the combination of HA + KC would be highly helpful in many texture-modifying applications.

Short communication: Evaluating the recovery potential of injured cells of Listeria innocua under product temperature-abuse conditions and passage through simulated gastrointestinal fluids.

Ice cream handling and serving conditions on the consumer side may result in temperature abuse before consumption. Under some extreme conditions, even the sporadic presence of injured bacterial cells might pose a health risk due to the possibility of recovery of those cells. We conducted this investigation to evaluate the potential of injured cells of Listeria innocua to recover under ice cream temperature abuse conditions and on exposure to simulated gastrointestinal (GI) fluids. Ice cream mix samples (42% total solids), spiked with 4 log10 cfu/g of Listeria innocua, were thermally treated at 69°C for 30 min. Potential heat-injured cells were recovered in buffered Listeria broth (BLEB), followed by isolation on Listeria-specific modified Oxford agar (MOX). The ice cream mix samples, containing potentially injured cells of Listeria innocua, were followed through overnight aging (7°C), freezing (-3.3°C), and overnight hardening (-40°C) steps to obtain the final ice cream samples. To simulate temperature abuse conditions, the samples were held for 12 h at 4.4°C, followed by 30 min at room temperature (22°C); this treatment was considered the first cycle of temperature abuse. To generate a worst-case scenario, the samples were exposed to 3 such consecutive temperature abuse cycles. At the end of each cycle, direct plating was done on MOX to recover viable cells, and BLEB enrichment verified the presence of potential injured cells. In addition, the ice cream samples, containing potential injured cells, were passed through simulated GI fluids. As a first step, samples were mixed (1:1) with simulated gastric fluids (pH 1.0 and 2.0 before mixing) and held at 37°C in a shaker incubator. Samples drawn at 15, 30, and 60 min were analyzed for viable and potential injured cells. To study the effect of sequential transit through simulated intestinal fluid, a mixture of ice cream and gastric fluid (1:1) from the gastric fluid experiment above was added to simulated intestinal fluid (pH 6.8) and held at 37°C. Samples were analyzed at 30 and 360 min for viable and potential injured cells. Three trials were conducted and the samples collected in duplicates. The temperature abuse or GI fluid exposure studies did not result in the recovery of potential injured cells of Listeria innocua in the ice cream samples under the conditions tested. Exposure to gastric fluids, however, did not eliminate the potential injured cells. Further studies are necessary to understand the exact risk implications of these findings.

Listeria cross contamination levels in raw ice cream mix can serve as a predictor of their potential presence as heat-injured cells.

Listeriosis is a life-threatening infection caused by foods contaminated with Listeria monocytogenes. Some of the major ice cream recalls in recent years reaffirm the ability of this food-borne pathogen to survive in diverse dairy processing environments and cause cross contamination. Inspection reports revealed certain lapses in implementing adequate hygienic practices for Listeria persistence in the processing environment, leading to cross contamination of ice cream. The higher levels of cross contamination of raw ice cream mix might result in random heat-injured cells when exposed to minimum heat treatment (69°C for 30 min). These heat-injured cells could later recover under abusive storage and handling conditions and pose a health risk. Evidence about the presence of injured cells in ice cream mix may thus prove useful to establish the overall Listeria risk, which was the aim of this study. Challenge studies were conducted to evaluate the dose-dependent presence of heat-injured cells of Listeria. Ice cream mix formulations of 4 different types (36, 40, 42, and 45% total solids) were inoculated at 2.0, 3.0, and 4.0 log cfu/g levels of Listeria innocua (an established surrogate). The dose levels were selected based on a likely cross contamination on the raw side from environmental Listeria, especially due to their resident nature and growth in harborage sites. The samples were exposed to minimum heat treatment (69°C for 30 min) and the survivors, including heat-injured cells, were enumerated using standard protocols. A binary logistic regression model was fitted for evaluating the severity of risk. The influence of total solids, water activity, and pH variability were also studied on Listeria survival. The enrichment protocol, using buffered Listeria enrichment broth, followed by plating on modified oxford agar and Rapid L'mono medium, revealed the random presence of heat-injured cells in buffered Listeria enrichment broth, only at the highest dose level of 4+ logs. Any potential risk from heat-injured cells was thus limited only to the highest levels of cross contamination, irrespective of the type of the mix. Significantly, none of the pasteurized ice cream mix samples supported the recovery of any heat-injured cells of Listeria during 72 h holding at 7°C, even at the highest dose level of 4+ logs, under the conditions of experimentation. The level of cross contamination (dose) emerged as a predictor of the potential presence of heat-injured cells of Listeria exposed to minimum pasteurization treatment.

Effect of hydrogen peroxide on improving the heat stability of whey protein isolate solutions.

Whey protein isolate (WPI) solutions (12.8%w/w protein) were treated with varying concentrations of H2O2 in the range of 0-0.144 H2O2 to protein ratios (HTPR) by the addition of the required quantity of H2O2 and deionized water. The samples were analyzed for heat stability, rheological properties, denaturation level of ß-lactoglobulin (ß-LG) and α-lactalbumin (α-LA). The samples treated with H2O2 concentration >0.072 (HTPR) showed significant improvement in the heat stability, and decreased whey protein denaturation and aggregation. The WPI solution treated with H2O2 (>0.072 HTPR) remained in the liquid state after heat treatment at 120°C, whereas the control samples formed gel upon heat treatment. Detailed analysis of these samples suggested that the improvement in the heat stability of H2O2 treated WPI solution was attributed to the significant reduction in the sulfhydryl-disulfide interchange reaction during denaturation of ß-LG and α-LA.