Proteolysis in goat cheese made from raw, pasteurized or pressure-treated milk

Evaluating the Quality of Cheese Slices Packaged with Na-Alginate Edible Films Supplemented with Functional Lactic Acid Bacteria Cultures after High-Pressure Processing

The aim of the current study was to assess the efficacy of Na-alginate edible films as vehicles for delivering lactic acid bacteria (LAB) with functional properties to sliced cheeses, with or without high-pressure processing (HPP). A three-strain LAB cocktail (Lactococcus lactis Τ4, Leuconostoc mesenteroides Τ25 and Lacticaseibacillus paracasei Τ26) was incorporated into Na-alginate solution in a final population of 9 log CFU/mL. The cheese slices (without or with HPP treatment at 500 MPa for 2 min) were packaged in contact with the LAB edible films (LEFs), and subsequently vacuum packed and stored at 4 °C. Cheese slices without the addition of films, with or without HPP treatment, were used as controls. In all cases, microbiological, pH and sensory analyses were performed, while the presence and the relative abundance of each strain during storage was evaluated using Random Amplified Polymorphic DNA-PCR (RAPD-PCR). In addition, organic acid determination and peptide analysis were performed using high-performance liquid chromatography. The results showed that in cheeses without HPP treatment, the microbiota consisted mostly of mesophilic LAB and lactococci (>7.0 log CFU/g), while HPP caused a reduction in the indigenous microbiota population of approximately 1−1.5 log CFU/g. In the LEF samples, the populations of mesophilic LAB and lactococci were maintained at levels of >6.35 log CFU/g during storage, regardless of the HPP treatment. Sensory evaluation revealed that the LEF samples without HPP had a slightly more acidic taste compared to the control, whereas the HPP-LEF samples exhibited the best organoleptic characteristics. RAPD-PCR confirmed that the recovered strains were attributed to the three strains that had been entrapped in the films, while the strain distribution during storage was random. Overall, the results of the study are promising since the functional LAB strains were successfully delivered to the products by the edible films until the end of storage.

Assessment of the Microbiological Quality and Biochemical Parameters of Traditional Hard Xinotyri Cheese Made from Raw or Pasteurized Goat Milk

Traditional hard Xinotyri cheese was manufactured using raw or pasteurized goat milk, without starter cultures, and the changes in microbiological and biochemical characteristics were studied during ripening and storage. Mesophilic lactic acid bacteria (LAB) predominated (>8.5 log CFU/g) in freshly fermented Xinotyri cheeses (pH 4.5–4.6), regardless of milk pasteurization. Enterobacteria, pseudomonads and staphylococci were suppressed below 6 and 4–5 log CFU/g in fresh cheeses from raw and pasteurized milk, respectively. Salmonella and Listeria spp. were absent in 25 g cheese samples. Coagulase-positive staphylococci exceeded the 5-log safety threshold in fresh raw milk cheeses, which also had 10-fold higher levels of enterococci than pasteurized milk cheeses. Non-LAB groups declined <100 CFU/g, whereas yeasts increased to 5–6 log CFU/g in both cheeses during ripening. Milk pasteurization affected the protein, fat, ash, moisture, nitrogen fractions, total free fatty acids and total free amino acids content of cheeses. Primary proteolysis, detectable by urea-PAGE, was more intense in raw milk cheeses than in pasteurized milk cheeses. However, the hydrophilic and hydrophobic peptides and their ratio in the water-soluble fraction were similar in both cheeses. Cheeses discriminated clearly according to the milk kind (raw, pasteurized) and the stage of ripening, based on the examined biochemical characteristics.

Effect of high pressure pre-treatment on raw ewes' milk and on subsequently produced cheese throughout ripening

BACKGROUND

Raw ewe's milk, as used to manufacture Serra da Estrela Protected Designation of Origin cheese, was pre-treated by high pressure processing (HPP), using previously optimized conditions (121 MPa for 30 min), aiming to evaluate its effect on milk technological properties for subsequent cheese production, namely the impact on resulting curd, whey and cheese throughout ripening.

RESULTS

The cheese yield increased 10.4% as a result of milk pre-treated by HPP, which also yielded inactivation of beneficial microbial groups. After 60 days of ripening, both treated and control cheeses showed no significant differences (P ≥ 0.05) with respect to quantified microbial load or basic physicochemical quality parameters.

CONCLUSION

HPP appears to be a promising non-thermal treatment for ewes' milk to inactivate contaminant bacteria but with no negative effect on lactic acid bacteria, which is very important for the unique characteristics of Serra da Estrela cheese. © 2020 Society of Chemical Industry.

High Hydrostatic Pressure as a Tool to Reduce Formation of Biogenic Amines in Artisanal Spanish Cheeses

Two artisanal varieties of cheese made in Spain, one made of ewes' raw milk and the other of goats' raw milk were selected to evaluate the effect of a high hydrostatic pressure (HHP) treatment at 400 MPa during 10 min at 2 °C on the formation of biogenic amines (BA). These conditions were applied at the beginning of the ripening (before the 5th day; HHP1) and in the case of ewes' milk cheeses also after 15th days (HHP15). BA formation was greatly influenced by HHP treatments in both types of cheese. HHP1 treatments significantly reduced the amounts of BA after ripening, being tyramine and putrescine the most affected BA in goats' milk cheeses and tyramine and cadaverine in ewes' milk cheeses. The BA reduction in the HHP1 samples could be explained by the significant decrease in microbiological counts, especially in the LAB, enteroccocci and enterobacteria groups at the beginning of ripening. The proteolysis in these samples was also affected reducing the amount of free amino acids. Although proteolysis in ewes' milk cheeses HHP15 was similar than in control samples a reduction of BA was observed probably because the decrease caused on microbial counts.

Chemical and instrumental approaches to cheese analysis

Overcoming the complexity of cheese matrix to reliably analyze cheese composition, flavor, and ripening changes has been a challenge. Several sample isolation or fractionation methods, chemical and enzymatic assays, and instrumental methods have been developed over the decades. While some of the methods are well established standard methods, some still need to be researched and improved. This chapter reviews the chemical and instrumental methods available to determine cheese composition and monitor biochemical events (e.g., glycolysis, lipolysis, and proteolysis) during cheese ripening that lead to the formation of cheese flavor. Chemical and enzymatic methods available for analysis of cheese composition (fat, protein, lactose, salt, nitrogen content, moisture, etc.) are presented. Electrophoretic, chromatographic, and spectroscopic techniques are also reviewed in the light of their application to monitor cheese ripening and flavor compounds. Novel instrumental methods based on Fourier-transform infrared spectroscopy that are currently being researched and applied to cheese analysis are introduced.