Flux and transmission of ß-casein during cold microfiltration of skim milk subjected to different heat treatments.

Raw skim milk was subjected to different heat treatments: thermization (65°C, 20 s), pasteurization (72°C, 15 s), and no heat treatment (milk was microfiltered using 1.4-µm membranes at 50°C for bacteria removal; 1.4 MF). The milk (thermized, pasteurized, and 1.4 MF) was cooled and stored at 2°C until processing (at least 24 h) with cold (∼6°C) microfiltration using a benchtop crossflow pilot unit (Pall Membralox XLAB 5, Pall Corp., Port Washington, NY) equipped with 0.1-µm nominal pore diameter ceramic Membralox membrane (ET1-070, α-alumina, Pall Corp.). The flux was monitored during the process, and ß-casein transmission and removal were calculated. The study aimed to indicate the conditions that should be applied to maximize ß-casein passage through the membrane during cold microfiltration (5.6 ± 0.4°C) of skim milk. The proper selection of heat treatment parameters (temperature, time) of the feed before the cold microfiltration process will increase ß-casein removal. It is not clear whether the difference in ß-casein transmission between 1.4 MF, thermized, and pasteurized milk results from the effect of heat treatment conditions on ß-casein dissociation from the casein micelles or on passage of ß-casein through the membrane. The values of the major parameters (permeation flux and tangential flow velocity, through the wall shear stress) responsible for a proper membrane separation process were considerably lower than the critical values. It seems that the viscosity of the retentate has a great effect on the performance of the microfiltration membranes for protein separation at refrigerated temperatures.

Short communication: Calcium partitioning during microfiltration of milk and its influence on rennet coagulation time.

Pasteurized skim milk was subjected to (1) microfiltration (MF) at 50°C and (2) MF at 6°C after storage at 2°C. The products of these treatments were retentate (RMF50) and permeate (PMF50), and retentate (RMF6) and permeate (PMF6), respectively. Additionally, RMF50 was subjected to (3) cold MF after water dilution to produce retentate (RMF6R) and permeate (PMF6R). Calcium migration was monitored by analyzing ionic, soluble, and total calcium content in feed, retentates, and permeates. The influence of calcium partitioning and calcium addition to feed, retentates, and retentates diluted with water was determined. Without CaCl2 addition, only skim milk, RMF50, and RMF6 coagulated after rennet addition. Higher true protein and casein content of RMF50 and RMF6 resulted in shorter time of renneting. The retentates diluted with water showed no signs of coagulation within 40 min. The addition of PMF6R to RMF50 did not affect rennet coagulation time within the observed 40 min in comparison to RMF50 + water. In general, higher CaCl2 addition resulted in shorter rennet coagulation time. Special attention should be paid to calcium partitioning during membrane processing of cheesemilk. The level of calcium addition should be adopted to calcium content in such cheesemilk, which is affected by conditions of the filtration process (i.e., concentration factor and temperature).

Modeling the growth of Listeria monocytogenes in mold-ripened cheeses.

This study presents possible applications of predictive microbiology to model the safety of mold-ripened cheeses with respect to bacteria of the species Listeria monocytogenes during (1) the ripening of Camembert cheese, (2) cold storage of Camembert cheese at temperatures ranging from 3 to 15°C, and (3) cold storage of blue cheese at temperatures ranging from 3 to 15°C. The primary models used in this study, such as the Baranyi model and modified Gompertz function, were fitted to growth curves. The Baranyi model yielded the most accurate goodness of fit and the growth rates generated by this model were used for secondary modeling (Ratkowsky simple square root and polynomial models). The polynomial model more accurately predicted the influence of temperature on the growth rate, reaching the adjusted coefficients of multiple determination 0.97 and 0.92 for Camembert and blue cheese, respectively. The observed growth rates of L. monocytogenes in mold-ripened cheeses were compared with simulations run with the Pathogen Modeling Program (PMP 7.0, USDA, Wyndmoor, PA) and ComBase Predictor (Institute of Food Research, Norwich, UK). However, the latter predictions proved to be consistently overestimated and contained a significant error level. In addition, a validation process using independent data generated in dairy products from the ComBase database (www.combase.cc) was performed. In conclusion, it was found that L. monocytogenes grows much faster in Camembert than in blue cheese. Both the Baranyi and Gompertz models described this phenomenon accurately, although the Baranyi model contained a smaller error. Secondary modeling and further validation of the generated models highlighted the issue of usability and applicability of predictive models in the food processing industry by elaborating models targeted at a specific product or a group of similar products.

Influence of flavors and stabilizers used on the preferences and properties of aerated tvarog curd cheese.

BACKGROUND: The Polish market for tvarog (curd cheese)-based products is growing continuously. The as- sortment of these goods include products with different textures, different additives and different flavours. In developing a successful food product one should ensure consumers are sufficiently involved during the development stages. Consumer-led food product development should be a standard procedure. The study aimed to develop a new variants of aerated tvarog spreads. METHODS: The research was divided into the following steps: evaluation of consumer pref- erences (questionnaire); production of aerated tvarog cheeses (different flavor variants); physico-chemical evaluation of new products (composition, TPA test); evaluation of new products by consumers (questionnaire with a 5-point scale); sensory evaluation of new products by an expert panel (2 types of questionnaire). RESULTS: Sweet tvarog spreads were characterized by a higher degree of aeration than cheeses with a savory flavor. The savory variants had a semi-liquid consistency after aeration. This could result from the addition of salt (6%) to flavor preparation. The products stabilized by gelatine showed a higher degree of aeration than the ones with starch. The savory cheeses showed lower hardness than sweet cheeses (P < 0.05). Both consum- ers and experts gave higher marks to the sweet variants of manufactured tvarog cheeses. CONCLUSIONS: The addition of salt to savory flavor preparation probably affected the texture of these products, which was semi-liquid. Texture plays a very important role in the development of new products and affects consumers’ preferences for the product.