Comparison of the Effects of High Hydrostatic Pressure and Pasteurization on Quality of Milk during Storage

Effect of Heat Pasteurization and Sterilization on Milk Safety, Composition, Sensory Properties, and Nutritional Quality

Milk pasteurization and sterilization by heat treatment have an exciting history, which followed steady steps. The main aim of these treatments is to extend the shelf life of milk by destroying pathogenic and milk spoilage bacteria. With developments in pasteurization techniques, the assurance of milk safety, and extended shelf life, pasteurized bovine milk has become a staple food, especially in Western diets. However, some concerns have recently been raised about the effect of pasteurization on the sensory properties and nutritional quality of milk, and alternative methods, such as high-pressure processing, are being investigated. The primary purpose of milk pasteurization and sterilization is summarized in this review article. The associated changes that affect the compositional, sensory, and nutritional quality of milk are discussed, with particular emphasis on protein structure and function. The review is concluded by considering alternative methods, their advantages and limitations, along with future prospects.

High-pressure processing and heat treatment of Murrah buffalo milk: Comparative study on microbial changes during refrigerated storage

This study aims to evaluate the effect of high-pressure processing (HPP) (500 and 600 MPa for 3 min and 5 min) on the microbial changes of Murrah buffalo milk in comparison to heat treatment (72 °C for 15 s of holding time) during refrigerated storage of 28 days. The results indicated that the total plate count (TPC) of raw milk at day 0 was 5.5 ± 0.6 log10 CFU/mL. At day 0, heat treatment lowered TPC to 3.9 ± 0.6, while HPP treatment was in the range of 4.1 ± 0.3 to 4.8 ± 0.6 log10 CFU/mL. Similarly, lowered yeast and mold count and lactic acid bacteria were noted in heat- and HPP-treated milk samples compared to the control sample during refrigerated storage. There were no Staphylococcus aureus and Escherichia coli detected in heat and HPP-treated samples. Heat or HPP treatment at 600 MPa for 5 min significantly extended the shelf-life of Murrah buffalo milk for three weeks at the refrigerated storage. In addition, HPP treatment did not alter the pH, lightness (L* value), protein, or fat content of Murrah buffalo milk during refrigerated storage. Hence HPP at 600 MPa for 5 min could be a suitable alternative to conventional heat treatment.

Preliminary Investigation towards the Use of Infrared Technology for Raw Milk Treatment

Infrared (IR) technology offers a promising solution for reducing microbiological loads in various food types while preserving their quality traits, such as flavour. However, research on IR's application in complex matrices is limited. Therefore, our preliminary study aimed to evaluate its effectiveness in sanitizing bovine raw milk. We assessed the bacterial count before and after IR treatment by comparing volatile organic compound profiles via headspace extraction and GC/MS analysis. Our findings showed that higher energy levels led to a greater bacterial reduction. IR85 was the most effective in reducing Coliforms and Enterobacteriaceae in non-homogenised samples, with a reduction ranging from -1.01 to >-2.99 and from -1.66 to -3.09 Log CFU/mL, respectively. IR60 and 70 showed no efficacy, while IR80 had intermediate but still satisfactory effect. IR85 notably affected volatile compounds, particularly increasing hexanal (from 0.08 to 4.21 ng g-1) and dimethyl sulphone (from 10.76 to 26.40 ng g-1), while IR80 better preserved the aroma profile. As a result, only IR80 was tested with homogenised raw milk, demonstrating significant bacterial reduction (from >2.39 to 3.06 Log CFU/mL for Coliforms and from 1.90 to >2.45 Log CFU/mL for Enterobacteriaceae) and maintaining the aroma profile quality.

Effect of the High Hydrostatic Pressure Process on the Microbial and Physicochemical Quality of Shalgam

The processing of shalgam requires the use of an appropriate processing technique due to yeast overgrowth. With advancements in processing technology, high hydrostatic pressure (HHP) as nonthermal and nonchemical preservation has gained attention for its potential. Response surface methodology with the Box-Behnken experimental design was used to make sense of the effects of HHP parameters, namely, pressure (100-500 MPa), temperature (20-40 °C), and time (5-15 min), on microbial and physicochemical factors (pH, total soluble solids, titratable acidity, bioactive compounds, color values). The reduction in the counts of total mesophilic aerobic bacteria, lactic acid bacteria, and yeast-mold increased proportionally with the increase of all pressure levels, application temperatures, and pressurization times (p < 0.05). Stability was maintained in pH, total solubility, and some color parameters such as L*, a*, ΔE, yellow color tone, and red color tone. All findings of the bioactive components (phenolic content, flavonoid content, antioxidant activity, and monomeric anthocyanin content) in the RSM design showed a significant change only in proportion to the square of time (p < 0.05). The optimum pressurization parameter combination of shalgam was determined as a pressure of 367 MPa, temperature of 31.9 °C, and process time of 10.5 min. Under these conditions, values of yeast and mold (Y&M) reduction, total flavonoid content (TFC), total monomeric anthocyanin contents (TMACs), titratable acidity (TA), and reducing sugar content (RSC) were obtained as 4.30 log cfu/mL, 192.89 mg QE/100 mL, 11.88 mg/100 mL, 2.41 glactic acid/L, and 6.78 mg/100 mL, respectively. In particular, the findings in the basic color parameters proved that there was no significant change in the saturated red color of the shalgam. Gallic acid, caffeic acid, chlorogenic acid, catechin, cyanidin-3-O-glucoside, malvidin-3-O-glucoside, and peonidin-3-O-glucoside derivatives are dominant phenolic and anthocyanin compounds, which are frequently found in turnip plants. No important losses in bioactive components were observed, despite changes in pressure and temperature parameters. The HHP method can be suggested to have great potential in the processing of shalgam (fermented turnip beverage) in terms of its ability to maintain the flavors, colors, and nutrients, in addition to ensuring microbiological safety when compared to other preservation methods.

Antimicrobial Activity of Eugenol Against Bacillus cereus and Its Application in Skim Milk

Bacillus cereus is a foodborne pathogen widely distributed in the large-scale catering industry and produces spores. The study explored the antibacterial activity, potential mechanism of eugenol against B. cereus, and spores with germination rate. The minimum inhibitory concentration (MIC; 0.6 mg/mL) of eugenol to six B. cereus strains was compared with the control; B. cereus treated with eugenol had a longer lag phase. Eugenol at a concentration of more than 1/2MIC decreased viable B. cereus (∼5.7 log colony-forming unit [CFU]/mL) counts below detectable limits within 2 h, and eugenol of 3MIC reduced B. cereus (∼5.9 log CFU/mL) in skim milk below detectable limits within 30 min. The pH values of skim milk were unaffected by the addition of eugenol. The ΔE values below 2 show that the color variations of skim milk were not visible to the human eye. For sensory evaluation, eugenol did not significantly affect the color or structural integrity of the skim milk. It had a negative impact on the flavor and general sensory acceptance of the treated milk. Eugenol hyperpolarized B. cereus cell membrane, decreased intracellular ATP concentration, and increased intracellular reactive oxygen species contents and extracellular malondialdehyde contents, resulting in the cell membrane of B. cereus being damaged and permeabilized, and cell morphology being changed. In addition, according to the viable count, confocal laser scanning microscopy, and spore morphology changes, eugenol reduced the germination rate of B. cereus spores. These findings suggest that eugenol can be used as a new natural antibacterial agent to control B. cereus and spores in the food production chain.

Extending the Shelf Life of Raw Milk and Pasteurized Milk with Plantaricin FB-2

Raw milk and pasteurized milk are characterized by a short shelf life, and drinking expired raw milk and pasteurized milk causes illness. In the study, Plantaricin FB-2 (extracted from Lactiplantibacillus plantarum FB-2) was added to liquid milk. By evaluating the microbial growth, acidity changes, protein content, and sensory changes in raw milk and pasteurized milk during storage, it was found that when Plantaricin FB-2 was added at 0.4 g/kg, the shelf life of raw milk was extended by 3 days (7 days if not added). The shelf life of pasteurized milk with Plantaricin FB-2 was extended to 31 days (25 days in the control group), and the optimal amount was 0.3 g/kg. This confirmed that Plantaricin FB-2 can effectively prolong the shelf life of raw and pasteurized milk. This study provides valuable information for the application of bacteriocins produced by Lactiplantibacillus plantarum in raw milk and pasteurized milk to improve their shelf life.