CHARACTERIZATION OF INTERACTION BETWEEN WHEY PROTEIN ISOLATE AND XANTHAN/CURDLAN HYDROGEL TO IMPROVE FREEZE-THAW STABILITY

Syneresis, the liquid separation from a food product, is one of the major challenges in the frozen food industry. It is often accelerated by unintentional temperature fluctuations, i.e. repeated freezing and thawing during distribution, transportation, storage, and consumption. It has been demonstrated that the combination of xanthan and curdlan is capable of reducing syneresis up to five freeze-thaw cycles (FTCs) with relatively stable rheological and textural properties. The present study aimed at developing an effective mixture of whey protein isolate (WPI) and xanthan-curdlan hydrogel complex (XCHC) to minimize moisture migration over multiple FTCs. The addition of XCHC to WPI solution significantly reduced the syneresis of heat-induced gels, increased the storage modulus (G') of the gels, reduced the minimum concentration of whey protein isolate required to form a gel, and minimized the discrepancies of G' in frequency sweep tests over 5 FTCs. By comparing the microstructure of mixed WPI-XCHC and pure WPI gels, it was found that XCHC served as a pore-forming agent, namely increasing the porosity, reducing the pore size, and consequently improving the gel's water retention over multiple FTCs. Results from dynamic rheological measurements showed that both G' and the gelation temperature of mixed WPI-XCHC complex were strongly pH-dependent. Moreover, the interactions between WPI and XCHC in aqueous solution were characterized. An edible coating solution containing the mixture of WPI, xanthan, and curdlan was tested on mushroom and green bell pepper. Fresh mushroom and green bell pepper samples treated with WPI-XCHC significantly prevented moisture migration after 10 days of frozen storage. The coating also decreased the changes of whiteness and greenness in mushroom and bell pepper, respectively, while significantly improved the firmness of bell peppers. Such information could provide useful guidelines when designing novel food products utilizing the unique properties provided by WPI-XCHC

Effect of acidic electrolyzed water-induced bacterial inhibition and injury in live clam (Venerupis philippinarum) and mussel (Mytilus edulis)

The effect of acidic electrolyzed water (AEW) on inactivating Escherichia coli O104:H4, Listeria monocytogenes, Aeromonas hydrophila, Vibrio parahaemolyticus and Campylobacter jejuni in laboratory contaminated live clam (Venerupis philippinarum) and mussel (Mytilus edulis) was investigated. The initial levels of bacterial contamination were: in clam 4.9 to 5.7log10CFU/g, and in mussel 5.1 to 5.5log10CFU/g. Two types of AEW were used for treatment time intervals of 1 and 2h: strong (SAEW) with an available chlorine concentration (ACC) of 20mg/L, pH=3.1, and an oxidation-reduction potential (ORP) of 1150mV, and weak (WAEW) at ACC of 10mg/L, pH=3.55 and ORP of 950mV. SAEW and WAEW exhibited significant inhibitory activity against inoculated bacteria in both shellfish species with significant differences compared to saline solutions treatments (1–2% NaCl) and untreated controls (0h). SAEW showed the largest inhibitory activity, the extent of reduction (log10CFU/g) ranged from 1.4–1.7 for E. coli O104:H4; 1.0–1.6 for L. monocytogenes; 1.3–1.6 for A. hydrophila; 1.0–1.5 for V. parahaemolyticus; and 1.5–2.2 for C. jejuni in both types of shellfish. In comparison, significantly (P<0.05) lower inhibitory effect of WAEW was achieved compared to SAEW, where the extent of reduction (log10CFU/g) ranged from 0.7–1.1 for E. coli O104:H4; 0.6–0.9 for L. monocytogenes; 0.6–1.3 for A. hydrophila; 0.7–1.3 for V. parahaemolyticus; and 0.8–1.9 for C. jejuni in both types of shellfish. Among all bacterial strains examined in this study, AEW induced less bacterial injury (~0.1–1.0log10CFU/g) and more inactivation effect. This study revealed that AEW (10–20mg/L ACC) could be used to reduce bacterial contamination in live clam and mussel, which may help control possible unhygienic practices during production and processing of shellfish without apparent changes in the quality of the shellfish. •Depuration with AEW reduces bacterial contamination in live clam and mussel.•Depuration with 1–2% NaCl may not cause a reduction in bacterial contamination.•AEW may help control possible unhygienic practices during processing of shellfish