Psychrotrophs in raw milk: effect on texture, proteolysis index, and sensory evaluation of smoked provolone cheese.

BACKGROUND: Provolone can be fresh or ripened, with its taste varying from sweet to spicy. The high psychrotrophic density of raw milk is associated with thermoresistant enzymes that can change cheese characteristics such as texture, promote sensory defects and decrease industrial yield. Two batches of provolone-type smoked cheese were produced from chilled raw milk with 3 log cfu mL-1 (Treatment 1) and 7 log cfu mL-1 (Treatment 2) of psychrotrophs. The psychrotrophic (21 °C for 25 h) and physical-chemical profile of the raw milk were determined. Cheeses were evaluated by fat level, primary and secondary proteolysis index, yield, protein profile (Urea-polyacrylamide gel electrophoresis), and texture (hardness, cohesiveness, elasticity, and chewiness) at 14, 30, and 60 days of storage time. Sensorially, the cheeses were evaluated (100 tasters/period) using the triangular test. RESULTS: The treatments did not influence proteolysis index, although maturation influenced the proteolytic depth index after 60 days. The psychrotrophic population influenced αs 1- and ß-casein fractions, while maturation time influenced αs 1- and γ-casein fractions. Treatment 2 induced a 3% reduction in cheese yield. Hardness and chewiness showed a linear and positive relationship with the milk's psychrotrophic load. There was a significant difference in the fat content of the cheeses, with Treatment 2 having a lower level. The triangular test showed no difference between the cheeses. CONCLUSION: Although the larger psychrotrophic population in raw milk was associated with superior values of hardness and chewiness, as well as an increase in protein fractions indicating that proteolysis was observed, the tasters did not identify sensorial differences between the cheeses. © 2020 Society of Chemical Industry.

Short communication: Effect of bactofugation of raw milk on counts and microbial diversity of psychrotrophs.

Bactofugation is a centrifugal process for removing spores of microorganisms from milk, especially when it is destined for cheese making. Other microorganisms may be removed in bactofugation. This study aimed to verify the effect of milk bactofugation on the counts and microbial diversity of psychrotrophs. The raw milk was preheated (≈55°C) before being bactofuged, and samples were collected from 3 batches of milk: refrigerated raw, preheated, and bactofuged, representing the immediate conditions before and after bactofugation. The mean psychrotrophic counts of the 3 batches were 3.08 (±1.69) × 106, 193 (±232), and 20 (±26) cfu/mL, respectively. Preheating was sufficient to eliminate 99.99% of the raw milk psychrotrophs, but bactofugation further reduced 89.66% of psychrotrophs from preheated milk. Lysinibacillus fusiformis was the most frequently isolated species (45.7%) among the psychrotrophs of raw milk and, proportionally, were more frequent in preheated (37.5%) and bactofuged (60%) milk. Bacillus invictae (20%), Enterococcus faecalis (10%), and Kurthia gibsonii (10%) were also isolated from bactofuged milk. Albeit in small numbers, psychrotrophic, thermoduric, and spore-forming bacteria with known proteolytic and lipolytic activity remained in the milk after bactofugation, which apparently had no effect on a specific population of microorganisms but proportionally reduced the entire psychrotrophic microbiota of raw milk.

Legal standards of milk delivered for processing in Brazil / Adequação aos padrões legais de leite entregue para beneficiamento no Brasil

Thresholds for Somatic Cell Counts (SCC) and Total Bacterial Counts (TBC) in refrigerated raw milk have been stricter in Brazil since July 2014. We evaluated whether the composition of 11,051 milk samples delivered to processing plants in Paraná state, Brazil, by cooperative dairy farms, complies with government requirements and established changes. Milk quality was evaluated from June to August 2014, from dairy farms in three states. Data were obtained by infrared spectroscopy and flow cytometry. SCC was highest in June (p<0.05), when the highest number of samples and mean values was observed that did not comply with legal standards. No samples obtained in July complied with the requirements. The city in Mato Grosso do Sul state was the only one that met the legal requirements throughout the period studied. TBC did not vary (p>0.05) in the trimester, and none of the cities presented values below the maximum TBC allowed. Protein, fat and non-fat solids obtained complied with legal requirements. Total solids and lactose varied among the months (p<0.05), with highest values for total solids in June and for lactose in August. Milk samples did not comply with minimal requirements for SCC and TBC, and were not adjusted to more rigid quality standards.

Limites de contagem de células somáticas (CCS) e contagem bacteriana total (CBT) em leite cru refrigerado estão mais estritos no Brasil desde Julho de 2014. Foram avaliadas 11051 amostras de leite entregues para beneficiamento no Estado do Paraná, Brasil, por produtores de leite e cooperados e verificou-se se estas atendiam aos requisitos governamentais e às mudanças estabelecidas. A qualidade do leite foi avaliada de Junho a Agosto de 2014 em fazendas leiteiras de três estados. Os dados foram obtidos por espectroscopia em infravermelho e citometria de fluxo. CCS foi superior em Junho (p<0,05), quando foi observado maior número de amostras e valores médios que não estavam de acordo com os padrões legais. A cidade do Estado de Mato Grosso do Sul foi a única que cumpriu com os limites legais requeridos ao longo do período. CBT não apresentou variação (p>0,05) ao longo do trimestre, e nenhuma das cidades apresentou valores dentro do limite estabelecido para CBT. Proteína, gordura e sólidos não gordurosos estavam de acordo com os limites requeridos. Sólidos totais e lactose variaram ao longo dos meses (p<0,05), com valores elevados para sólidos totais em Junho e para lactose em Agosto. Amostras de leite não estavam de acordo com os requisitos mínimos de CCS e CBT, e não estão ajustadas aos padrões de qualidade mais rígidos.