The impact of four different regimes of heat sterilization (110C for 100 min, 115C for 32 min, 120C for 10 min and 125C for 3.2 min) on the properties of processed cheeses was evaluated. Also, nonsterilized samples were analyzed. Samples without and with the addition of lactose (0.5–2.0% w/w) were studied because lactose might be present in raw materials at various concentrations and might significantly affect processed cheese quality. All the sterilization regimes ensured inactivation of microflora. When the sterilization temperature was reduced (with simultaneously prolonged exposure time) the samples showed worse sensory properties. Significant hydrolytic changes of proteins and larger amino acid losses were also detected. The smallest changes were noted in products treated at 125C for 3.2 min. The heat treatment at 120C for 10 min caused acceptable modification of cheese properties. Addition of lactose higher than 1.0% w/w was found unsuitable for the production of sterilized processed cheeses. PRACTICAL APPLICATIONS Processed cheese is a natural cheese‐based foodstuff manufactured using heat treatment (especially at 80–100C). Sterilized processed cheese is a specific product with prolonged shelf life, which could be used either in everyday life or for military and rescue team boarding during operations (Buňka et al. 2004). This product is manufactured in many countries but only limited scientific information about its quality and properties is available. Powdered skim milk and whey (used mainly for cutting the costs of the ingredients), which contain high amounts of lactose, are widely used in production of processed cheese. Lactose can show a deteriorating effect on the quality of processed cheeses, especially after application of severe heat treatment. Results of this study could be useful for setting sterilization time and temperature in order to manufacture products with high nutritive and sensory value. Moreover, a comparative study exploring acceptable lactose concentration value was carried out.

This study reports the development of selected indicators affecting changes in food quality and safety of selected long-life canned (Szeged goulash, canned chicken meat, pork pâté, canned tuna fish) and dehydrated (instant goulash soup) food during a two-year storage experiment at four different temperatures. The storage temperatures were selected to represent Arctic (−18 °C), temperate (5 °C), subtropical (25 °C) and tropical (40 °C) climatic zones where such food is likely to be stored during, for example, humanitarian and military missions. Microorganism amounts below the detection limit (p < 0.05), regardless of the storage temperature (p ≥ 0.05), were monitored in canned samples. The contents of dry matter, fat and proteins did not change during storage, regardless of the storage temperature (p ≥ 0.05). During the 24-month storage, all food showed an increase in the level of ammonia (p < 0.05) and the TBARS-value (p < 0.05), whereas the rate of increase in both parameters was significantly higher at higher storage temperatures (p < 0.05). The losses of individual amino acids during storage ranged from 5% rel. calculated on the amino acid contents in Month “0” up to 15% rel. (p < 0.05). With storage temperatures above the freezing point, the hardness values decreased with the increase in the storage temperature (p < 0.05) and prolongation of the storage period (p < 0.05). Moreover, with temperatures of −18 °C, the development of hardness, measured as the “decrease rate”, was significantly higher compared to the absolute values.

Lazárková Z., Buňka F., Buňková L., Valášek P., Kráčmar S., Hrabě J. (2010): Application of different sterilising modes and the effects on processed cheese quality. Czech J. Food Sci., 28: 168-176.The aim of the present work is to evaluate the impacts of four different sterilising modes (110°C 100 min, 115°C 32 min, 120°C 10 min, and 125°C 3.2 min -with a constant lethal effect on microorganisms) on some chemical (pH, total and bio-available lysine, and ammonia content), microbiological, and sensory (shade and acceptability) properties of processed cheese depending on the lactose additions (0.0-2.0% w/w). All sterilising modes used were sufficient to inactivate the microorganism groups observed (total number of microorganisms, colony forming units of yeasts and/or moulds, number of spore-forming microorganisms). The falling sterilisation temperature kept for an adequately prolonged period of time caused darkening of the processed cheese and a decline of their acceptability. Consequently, greater losses of lysine and ammonia content increase occurred when the sterilisation temperature decreased. Compared to non-sterilised products, the smallest changes were detected in the cheese treated with temperatures 125°C for 3.2 min, and 120°C for 10 minutes. The decrease of the processed cheese quality was more apparent with the growing lactose concentration.

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The current study was conducted to evaluate the effect of the addition of selected hydrocolloids [agar (AG), κ-carrageenan (KC), or gelatin (PG); as a total replacement for emulsifying salts] on the viscoelastic properties and microstructure of processed cheese (PC) samples during a storage period of 60 days (at 6 ± 2 °C). In general, PC viscoelastic properties and microstructure were affected by the addition of hydrocolloids and the length of storage time. The evaluated PC reported a more elastic behavior (G′ > G″) over the viscous one. The highest values of viscoelastic moduli (G′; G″; G*) were recorded for PC samples manufactured with KC addition, followed by those prepared with AG and PG. The control sample presented values of viscoelastic moduli similar to those of the PG sample. All PC samples tested had fat globule size values lower than 1 μm. Moreover, PC with AG and KG addition presented similar microstructures and sizes of fat globules.

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