Inactivation of natural microorganisms in litchi juice by high-pressure carbon dioxide combined with mild heat and nisin

Enhancement effect of carvacrol on yeast inactivation by mild pressure carbon dioxide

Saccharomyces cerevisiae is one of the common spoilage microorganisms in fruit juices. This paper investigated the influences of carvacrol on S. cerevisiae inactivation by mild pressure carbon dioxide (MPCO2). The results demonstrated that carvacrol synergistically enhanced the antifungal activity against S. cerevisiae of MPCO2. With the increase of carvacrol concentration (20-160 µg/mL), CO2 pressure (1.5-3.5 MPa), process temperature (20-40 °C), and treatment time (15-60 min), the inactivation effect of carvacrol combined with MPCO2 on S. cerevisiae was gradually increased and significantly stronger than either single treatment. In the presence of carvacrol, MPCO2 severely disordered the plasma membrane of S. cerevisiae, including the increase of membrane permeability, and the loss of membrane potential and integrity. MPCO2 and carvacrol in combination also aggravated the mitochondrial depolarization of S. cerevisiae and reduced intracellular ATP and protein content. This study suggests the potential of carvacrol and pressurized CO2 as an alternative technology for food pasteurization.

How to comprehensively improve juice quality: a review of the impacts of sterilization technology on the overall quality of fruit and vegetable juices in 2010-2021, an updated overview and current issues

Fruit and vegetable juices (FVJ) are rich in nutrients, so they easily breed bacteria, which cause microbial pollution and rapid deterioration of their quality and safety. Sterilization is an important operation in FVJ processing. However, regardless of whether thermal sterilization or non-thermal sterilization is used, the effect and its impact on the overall quality of FVJ are strongly dependent on the processing parameters, microbial species, and FVJ matrix. Therefore, for different types of FVJ, an understanding of the impacts that different sterilization technologies have on the overall quality of the juice is important in designing and optimizing technical parameters to produce value-added products. This article provides an overview of the application of thermal and non-thermal technique in the field of FVJ processing over the past 10 years. The operating principle and effects of various technologies on the inactivation of microorganisms and enzymes, nutritional and functional characteristics, physicochemical properties, and sensory quality of a wide range of FVJ are comprehensively discussed. The application of different combinations of hurdle technology in the field of FVJ sterilization processing are also discussed in detail. Additionally, the advantages, limitations, and current application prospects of different sterilization technologies are summarized.

Investigating the microbial inactivation effect of low temperature high pressure carbon dioxide and its application in frozen prawn (Penaeus vannamei)

During the pandemic of coronavirus disease 2019, the fact that frozen foods can carry the relevant virus raises concerns about the microbial safety of cold-chain foods. As a non-thermal processing technology, high pressure carbon dioxide (HPCD) is a potential method to reduce microbial load on cold-chain foods. In this study, we explored the microbial inactivation of low temperature (5-10 °C) HPCD (LT-HPCD) and evaluated its effect on the quality of prawn during freeze-chilled and frozen storage. LT-HPCD treatment at 6.5 MPa and 10 °C for 15 min could effectively inactivate E. coli (99.45%) and S. aureus (94.6%) suspended in 0.85% NaCl, SARS-CoV-2 Spike pseudovirus (>99%) and human coronavirus 229E (hCoV-229E) (>1-log virus tilter reduction) suspended in DMEM medium. The inactivation effect of LT-HPCD was weakened but still significant when the microorganisms were inoculated on the surface of food or package. LT-HPCD treatment at 6.5 MPa and 10 °C for 15 min achieved about 60% inactivation of total aerobic count while could maintain frozen state and quality of prawn. Moreover, LT-HPCD treated prawn exhibited significant slower microbial proliferation and no occurrence of melanosis compared with the untreated samples during chilled storage. A comprehensive quality investigation indicated that LT-HPCD treatment could maintain the color, texture and sensory of prawn during chilled or frozen storage. Consequently, LT-HPCD could improve the microbial safety of frozen prawn while maintaining its original quality, and could be a potential method for food industry to improve the microbial safety of cold-chain foods.

Shelf life of tempeh processed with sub-supercritical carbon dioxides

Tempeh, a fermented soybean-based food originally from Indonesia, is a remarkably nutritious functional food with health benefits. Unfortunately, tempeh is highly perishable, with a shelf life of 24 – 48 hours. The goal of this research was to evaluate the possibility of a sub-supercritical CO2 technique to increase the shelf life of tempeh by measuring the changes in the L* (lightness) value and texture of tempeh via application of a kinetic approach and, based on the observations, to estimate its shelf life. Tempeh was processed with sub-supercritical CO2 at 6.3 MPa for 10 min, then together with unprocessed tempeh (control), stored for 5 days at temperatures of 20, 30 and 40 °C. The Accelerated Self-Life Test (ASLT) with the Arrhenius model was used to measure the shelf life of processed and control tempeh. The calculated shelf life of processed tempeh using the ASLT by the Arrhenius method was 2.43 days at 20 °C, 3.7 days at 30 °C and 1.4 days at 40 °C, and the shelf life of unprocessed tempeh was 3.33 days at 20 °C, 2.90 days at 30 °C and 2.56 days at 40 °C. The conclusion was that the use of sub-supercritical CO2 at 6.3 MPa for 10 min increased the shelf life of tempeh stored at 30 °C.

Application of nisin-assisted thermosonication processing for preservation and quality retention of fresh apple juice

The effects of thermosonication (TS) and 100 ppm nisin-assisted TS (TS + nisin) on the inactivation of naturally occurring microorganisms, retention of nutritional quality and extension of shelf life of fresh apple juice were evaluated, with nisin and mild heat (nisin + MH) treatments as control. Fresh apple juice was addressed by nisin + MH, TS and TS + nisin at 37, 42, 47, and 52 °C for 5-40 min. After processing, microbial growth was evaluated during storage at 8 °C at every 5 days. Temperature played a vital role in the inactivation of aerobic bacteria and yeasts and molds by TS and TS + nisin, higher temperature up to 52 °C could cause a considerable inactivation of microbial cells in apple juice. As apple juice was subjected to TS and TS + nisin at 52 °C for 30 min, retention of original quality including 89% ascorbic acid, non-visible color change, no significant alteration in BD, pH, TA and TSS values of fresh apple juice, and extension shelf life to 15 d at 8 °C were obtained. Nisin exhibit additional inactivation effect of aerobic bacteria in apple juice while not obviously effect on yeast and molds. These results indicated a potential application of TS and TS + nisin (100 ppm) to produce fresh-like quality apple juice and/or to extend its shelf life.

Nisin as a Food Preservative: Part 1: Physicochemical Properties, Antimicrobial Activity, and Main Uses

Nisin is a natural preservative for many food products. This bacteriocin is mainly used in dairy and meat products. Nisin inhibits pathogenic food borne bacteria such as Listeria monocytogenes and many other Gram-positive food spoilage microorganisms. Nisin can be used alone or in combination with other preservatives or also with several physical treatments. This paper reviews physicochemical and biological properties of nisin, the main factors affecting its antimicrobial effectiveness, and its food applications as an additive directly incorporated into food matrices.

Escherichia coli inactivation by pressurized CO2 treatment methods at room temperature: Critical issues

This study aims to increase the inactivation efficiency of CO2 against Escherichia coli under mild conditions to facilitate the application of pressurized CO2 technology in water disinfection. Based on an aerating-cycling apparatus, three different treatment methods (continuous aeration, continuous reflux, and simultaneous aeration and reflux) were compared for the same temperature, pressure (0.3-0.7MPa), initial concentration, and exposure time (25min). The simultaneous aeration and reflux treatment (combined method) was shown to be the best method under optimum conditions, which were determined to be 0.7MPa, room temperature, and an exposure time of 10min. This treatment achieved 5.1-log reduction after 25min of treatment at the pressure of 0.3MPa and 5.73-log reduction after 10min at 0.7MPa. Log reductions of 4.4 and 5.0 occurred at the end of continuous aeration and continuous reflux treatments at 0.7MPa, respectively. Scanning electron microscopy (SEM) images suggested that cells were ruptured after the simultaneous aeration and reflux treatment and the continuous reflux treatment. The increase of the solubilization rate of CO2 due to intense hydraulic conditions led to a rapid inactivation effect. It was found that the reduction of intracellular pH caused by CO2 led to a more lethal bactericidal effect.

Role of peach proteins in juice precipitation induced by high pressure CO2

To better understand the role of peach proteins in juice precipitation induced by high pressure CO2 (HPCD), proteins extracted from peach juice were subjected to HPCD and heat, and changes in particle size distribution (PSD) and structure were investigated. PSD analysis showed aggregations of proteins were both induced by HPCD and heat, but HPCD induced a stronger aggregation. The endotherm of HPCD- and heat-treated proteins moved to lower temperature, indicating that higher-order structures were altered after treatments. Furthermore, proteins related to HPCD- and heat-induced precipitation were analyzed by proteomics and bioinformatics. It was found that proteins with low content of α-helix and hydrogen bonds were more inclined to precipitate under HPCD, and HPCD precipitated proteins with more compact structures than heat, which might cause the stronger aggregation of proteins by HPCD. In conclusion, HPCD could induce the aggregation of peach proteins by destroying higher-order structures, which contributes to juice precipitation.

Membrane Damage Induced by Supercritical Carbon Dioxide in Rhodotorula mucilaginosa

To clarify the mechanism of microbial inactivation by supercritical carbon dioxide (SCCO2), membrane damage of Rhodotorula mucilaginosa was investigated within specific pressure (10 Mpa), temperature (37 °C), and treatment time (10-70 min) ranges, including cell morphological structure, membrane permeability and fluidity. SEM and TEM observations showed morphological changes in the cell envelope and intracellular organization after SCCO2 treatment. Increase of membrane permeability was measured as increased uptake of the trypan blue dye with microscopy, and leakage of intracellular substances such as UV-absorbing materials and ions by determining the change of protein and electrical conductivity. The SCCO2 mediated reduction in CFU ml(-1) was 0.5-1 log higher at 37 °C and 10 MPa for 60 min in Rose Bengal Medium containing 4 % sodium than a similar treatment in Rose Bengal Medium. Membrane fluidity analyzed by fluorescence polarization method using 1,6-diphenyl-1,3,5-hexatriene showed that the florescence polarization and florescence anisotropy of the SCCO2-treated cells were increased slightly and gently compared with the untreated cells. The correlation between membrane damage and death of cells under SCCO2 was clear, and the membrane damage was a key factor induced the inactivation of cells.