High-pressure processing of berry and other fruit products: implications for bioactive compounds and food safety.

Fruits contain a variety of nutrients and polyphenols that are associated with health benefits. Year-round availability of fresh fruits is limited due to perishability. Processing fruits extends shelf life. Individual quick-frozen fruit is the most common for fruits, but nowadays, processing fruits into beverages offers extended shelf life and new market opportunities. Conventional thermal processing is an effective method for producing safe, extended shelf life, and shelf-stable products, including beverages. However, the high temperatures negatively affect nutritive quality by destroying essential nutrients and biologically active "non-essential" components such as polyphenols. Therefore, novel technologies that can preserve nutrient quality while ensuring food safety are warranted. In this review, the application of high-pressure processing (HPP) for preserving nutrients and phytochemicals while ensuring microbiological safety in beverages and other foods containing fruits is discussed.

Kinetics of Bacillus cereus spore inactivation in cooked rice by combined pressure-heat treatment.

The efficacy of pressure-heat treatment was evaluated for the inactivation of Bacillus cereus spores in cooked rice. The spores of B. cereus ATCC 9818 were inoculated (1.1 × 10(8) CFU/g) in a parboiled rice product (pH 6.0, water activity of 0.95) and inactivated to an undetectable level (<10 CFU/g) by treatment of 600 MPa and process temperatures of 60 to 85 °C or 0.1 MPa and 85 °C. Kinetic inactivation parameters were estimated with linear and nonlinear models. The potential recovery of injured bacteria was also evaluated during storage of the treated product for 4 weeks at 4 and 25 °C. Depending on the process temperature, a 600-MPa treatment inactivated spores by 2.2 to 3.4 log during the 30-s pressure come-up time, and to below the detection limit after 4- to 8-min pressure-holding times. In contrast, a 180-min treatment time was required to inactivate the spores to an undetectable level at 0.1 MPa and 85 °C. The decimal reduction time of spores inactivated by combined pressure-heat treatment ranged from 1.08 to 2.36 min, while it was 34.6 min at 85 °C under atmospheric conditions. The nonlinear Weibull model scale factor increased, and was inversely related to the decimal reduction time, and the shape factor decreased with increasing pressure or temperature. The recovery of injured spores was influenced by the extent of pressure-holding time and process temperature. This study suggests that combined pressure-heat treatment could be used as a viable alternative to inactivate B. cereus spores in cooked rice and extend the shelf life of the product.

Combined pH and high hydrostatic pressure effects on Lactococcus starter cultures and Candida spoilage yeasts in a fermented milk test system during cold storage.

The combined effects of high pressure processing (HPP) and pH on the glycolytic and proteolytic activities of Lactococcus lactis subsp. lactis, a commonly used cheese starter culture and the outgrowth of spoilage yeasts of Candida species were investigated in a fermented milk test system. To prepare the test system, L. lactis subsp. lactis C10 was grown in UHT skim milk to a final pH of 4.30 and then additional samples for treatment were prepared by dilution of fermented milk with UHT skim milk to pH levels of 5.20 and 6.50. These milk samples (pH 4.30, 5.20 and 6.50) with or without an added mixture of two yeast cultures, Candida zeylanoides and Candida lipolytica (10(5) CFU mL(-1) of each species), were treated at 300 and 600 MPa (≤20°C, 5 min) and stored at 4°C for up to 8 weeks. Continuing acidification by starter cultures, as monitored during storage, was substantially reduced in the milk pressurised at pH 5.20 where the initial titratable acidity (TA) of 0.40% increased by only 0.05% (600 MPa) and 0.10% (300 MPa) at week 8, compared to an increase of 0.30% in untreated controls. No substantial differences were observed in pH or TA between pressure-treated and untreated milk samples at pH 4.30 or 6.50. The rate of proteolysis in milk samples at pH values of 5.20 and 6.50 during storage was significantly reduced by treatment at 600 MPa. Treatment at 600 MPa also reduced the viable counts of both Candida yeast species to below the detection limit (1 CFU mL(-1)) at all pH levels for the entire storage period. However, samples treated at 300 MPa showed recovery of C. lipolytica from week 3 onwards, reaching 10(6)-10(7) CFU mL(-1) by week 8. In contrast, C. zeylanoides did not show any recovery in any of the pressure-treated samples during storage.