Egg yolk undergoes an irreversible gelation process at temperatures below −6 °C, which greatly impairs its application and increases its apparent viscosity. This work was aimed to investigate the effect of salt and pH in preventing the gelation of frozen-thawed egg yolk. Before freezing, 5% of salt was added into the pasteurized liquid egg yolk, then pH was adjusted to different levels (5.7, 6.0 and 6.3) with citric acid. After that, the yolk was stored at −18 °C for four weeks. Rheological and thermal properties of the fresh and frozen-thawed egg yolk were measured. In addition, the colour, turbidity and emulsifying properties were also determined. The results showed that pH of all samples increased during frozen storage, but at different rates. The combination of 5% of salt and pH at 6.0 and 6.3 could prevent the gelation, resulting in rheological properties more like the fresh liquid egg yolk. In addition, emulsifying properties also obtained better results for treated yolk. Moreover, L* value of treated egg yolk was higher before freezing and became lower after storage compared to control. The results of this work found that the combination of 5% of salt and adjusted pH could prevent the gelation of frozen-thawed liquid yolk.

In this study, the effects of high hydrostatic pressure treatment on the quality characteristics and the protein structure of vacuum-packed fresh pork and wild boar meats were investigated. Based on the results, an optimal pressure value was determined that would not cause the sensory properties of the treated flesh to differ from that of the untreated fresh meats but would effectively contribute to the extension of shelf life. The conclusion was made that high hydrostatic pressure treatment performed at 200 MPa did not lead to the denaturation of meat proteins and had no significant effect on the pH value or the color parameters. However, the shelf life of the meat could be extended by a week due to the two-orders-of-magnitude germicidal effect of the treatment.

The aim of this study was to investigate the utilization of buttermilk, a by-product of butter production, in ice cream. Butterfly pea flower, which provides natural coloring and antioxidant properties, was added to buttermilk for investigating its improving effect on the techno-functional and sensory attributes of ice cream. Ice cream mixes were prepared with varying buttermilk concentrations (0%, 20%, 40%, 60%, 80%, 100%) as the first factor of the research. In addition, the effect of fermentation was also investigated as the second factor of the experiment. The ingredients included buttermilk, milk, cream, sucrose, dextrose, locust bean gum, butterfly pea flowers, and vanilla extract. The preparation involved the extraction of the butterfly flowers, fermentation in case of the fermented samples, homogenization, pasteurization, freezing, and hardening. Quality attributes such as dry matter content, pH, color, rheological properties of the ice cream mixes, overrun, melting properties, and ice cream hardness were analyzed to determine the maximal substitution level of milk by buttermilk without compromising ice cream quality. Our results explore the impact of buttermilk content and fermentation on the techno-functional properties of ice cream. As buttermilk concentration increased, dry matter content decreased, ranging from 34.4 g/100 g at 0% buttermilk to 31.9 g/100 g at 100% buttermilk. pH levels were lower in the fermented samples, decreasing from 6.5 in the non-fermented to 4.6 in the fermented samples. L* decreased with higher buttermilk content, while a* and b* values increased slightly. The butterfly pea flower provided a blue hue across all samples; the blue hue increased by 20% with a higher buttermilk content. Increasing the buttermilk concentration led to a 40% decrease in the yield stress and consistency coefficient, indicating a less viscous mix. The flow behavior index slightly increased, suggesting a more Newtonian-like flow at higher buttermilk levels. Overrun decreased with a higher buttermilk content, from 45% at 0% buttermilk to 30% at 100% buttermilk, indicating reduced air incorporation. The meltdown rate increased with a higher buttermilk content, meaning the ice cream melted more rapidly. The hardness of the ice cream decreased as buttermilk concentration increased, from 15 N at 0% buttermilk to 10 N at 100% buttermilk. The fermented sample groups were on average 44% harder than the non-fermented sample groups. The findings suggest that up to 100% of buttermilk can effectively replace milk in ice cream formulations without compromising quality, providing a sustainable and health-beneficial use for this dairy by-product.

A folyékony tojástermékek viszonylag rövid ideig eltarthatók, ugyanis a tojásban megtalálható fehérjék alacsony hőmérsékletű hődenaturációja miatt csak alacsony hőmérsékleten hőkezelhetők. A néhány hetes fogyaszthatósági időt meg-növelhetjük, ha a hőkezelést egyéb tartósítási eljárásokkal kombináljuk. Egy lehetséges megoldás a tojáslevek fagyasztása, és fagyasztva tárolása a hőkezelést követően. A tojásfehérje reológiai tulajdonságai nem változnak a fagyasztás hatására, azonban a tojássárgája a fagyasztás során egy irreverzibilis gélesedésen megy keresztül. A tojássárgájában végbemenő változások és azok megelőzése krioprotektív hatású anyagokkal intenzíven kutatott témakör, azonban a teljes tojáslében végbemenő változásokról nagyon kevés információval rendelkezünk. Kutatásunkban ezért azt vizsgáltuk, hogy hogyan változnak a teljes tojáslé különböző tulajdonságai fagyasztás, illetve hosszú távú fagyasztva tárolás hatá-sára. A teljes tojáslevet lassú fagyasztással és felengedtetéssel vizsgáltuk 150 napig tartó kísérletünkben. Vizsgáltuk a friss és fagyasztott-felengedtetett teljestojáslé-minták színét tristimulusos színmérő készülékkel, pH-ját, reológiai tulajdonsá-gaikat rotációs reométerrel felvett folyásgörbék összehasonlításával, kalorimetrikus tulajdonságaikat differenciális pásztázó kaloriméterrel és sütési tulajdonságaikat a tojáslevekből készített piskóta állományának mérésével. Kutatásunk során megállapítottuk, hogy a fagyasztás és a fagyasztva tárolás során a teljes tojáslé világossági tényezője szignifikánsan megváltozik, a minták világosabbá válnak. Ezenkívül a pH is növekvő tendenciát mutat. A reológiai tulajdonságok szignifikáns változáson esnek át, amely kisebb mértékű, mint a tojássárgájalé esetében. A nyírófeszültség, illetve a konzisztencia koefficiens nő, a fagyasztott-elengedtetett minták megközelítőleg newtoni folyadékként vi-selkednek, illetve a minták vizuális értékelése során látható, hogy az állományuk megváltozik. Ezenkívül megállapítottuk, hogy a teljes tojáslé fehérjéi denaturációt vagy aggregációt szenvednek el a fagyasztás és a fagyasztva tárolás során, melynek következtében a tojáslé felverése nehezebbé vált, és az elkészített piskóta állománya gumissá lett.

Freeze–thaw cycles lead to undesirable gelation in egg yolk, which negatively affects its functional properties, restricting its application in the food industry. This study aimed to investigate whether enzymatic treatment can prevent the freeze-induced gelation of egg yolk, thereby maintaining its desirable quality attributes. Egg yolk samples were treated with an enzyme preparation (Biocatalysts Flavorpro™ 750MDP) at concentrations of 0.05, 0.3, and 0.5 w/w%, homogenized, and incubated at 40 °C for 120 min, followed by rapid cooling and freezing at −24 ± 1 °C for 60 d. Control samples without enzyme treatment were subjected to the same processing steps as the other samples. After thawing, all samples were analyzed for pH, color, rheological and thermophysical properties, turbidity and visual appearance. The results demonstrated that although enzymatic treatment and its combination with freezing significantly altered color, turbidity, rheological and thermophysical properties of egg yolk, it effectively inhibited freezing-induced gel formation, particularly at 0.3 w/w%. The parameters characterizing rheological behavior—yield stress, consistency coefficient, and flow behavior index—were preserved close to those of fresh yolk after the freeze–thaw process. These findings suggest that exopeptidase treatment is a promising approach for controlling freeze–thaw-induced gelation in egg yolk, supporting its wider use in frozen and processed egg products.