Advances in thermosonication for the inactivation of endogenous enzymes in foods

The main objective of food pasteurization is to inactivate pathogens and reduce spoilage organisms. For certain foods (e.g. orange juice) and in particular with emerging non-thermal technologies such as ultrasound and high pressure processing, endogenous and deteriorative enzymes can be very resistant. Therefore, enzymes should also be used as pasteurization references to avoid spoilage of processed foods during storage. Thus, endogenous food enzymes should be inactivated to increase its shelf life. In this chapter a review of the effects of thermo-sonication (simultaneous ultrasound and heat) on food enzymes was carried out. The ultrasound treatment denatures the enzyme, resulting in enzyme conformational changes and decrease in its activity. A variety of foods has been processed by ultrasound without heat, thermos-sonication and mano-thermo-sonication and the effect on enzymes is reviewed. Thermo-sonication and mano-thermo-sonication are recommended for enzyme inactivation, since ultrasound at room temperature is often ineffective against most food enzymes. The most relevant plant endogenous enzymes are pectinmethylesterase (PME), polygalacturonase (PG), polyphenoloxidase (PPO) and peroxidase (PRO), which are important for fruit and vegetable products. In addition lactoperoxidase (LPO), γ-glutamyltranspeptidase (GTP) and alkaline phosphatase (AP) from milk and dairy products are also reviewe

Hydroxyproline and proline content of cell walls of sunflower, peanut and cotton grown under salt stress

Proline and hydroxyproline content of the cell walls of peanut (Arachis hypogea L. cv. Shulamit), cotton (Gossypium hirsutum L. cv. sj) and sunflower (Helianthus annuus L. cv. Saffola SO222) were determined. Proline concentration in the leaves of all plants species tested was approximately 110 nmol · mg-1 dry matter and higher than in the root and stem. Hydroxyproline concentration was highest in the root of all species tested and was between 30 and 60 nmol·mg-1 dry matter. This was 5-10 times higher than the concentration in the stem and leaf. There was no significant effect of salt stress on proline and hydroxyproline concentration in "purified cell wall fraction" of sunflower. Salt stress (100 mmol·l-1NaCl) reduced substantially plant growth of 53-day-old sunflowers, stem volume decreased from 21.3 ± 5.2 ml to 3.8 ± 1.6 ml, dry matter content of stem decreased from 719 ± 186 mg to 88±33 mg and the number of leaves per plant decreased from 18 to 13. These results suggest that inhibition of plant growth, by salt stress, was accompanied by inhibition of cell wall proteins (extensins) synthesis. Therefore, changes in the physicochemical properties of cell wall accompanying the osmotic adjustment should be sought in other posttranslational modifications of extensin(s), either glycosylation or inter-and/or intramolecular cross-linking in the cell wall

Polyphenoloxidase in fruit and vegetables: inactivation by thermal and non-thermal processes

The activity of endogenous quality degrading enzymes together with spoilage microorganisms and/or other non-enzymatic (i.e. oxidative reaction) reactions considerably shorten the shelf life of fruit and vegetable products. Enzymatic browning by polyphenoloxidase (PPO) causes color and flavor degradation of fruit and vegetable products during processing and storage. This imposes significant economy loss to the fruit/vegetable processing industry (e.g. juices). PPO is conventionally inactivated by heat or thermal processing in the range of 80 to 90 °C. As consumers have been choosing preservative free and fresh-like foods, there is global trend to reduce the use of chemical food additives. Therefore, alternative non-thermal food preservation technologies such as high pressure processing (HPP), ultrasound processing (US) and pulsed electric fields (PEF) have been researched and implemented commercially. In this chapter a review of the effect of thermal and major non-thermal food preservation technologies (alone or combined with moderate heat) on PPO inactivation was carried out, resumed in five original Tables and discussed. The information collected can assist fruit/vegetable manufacturers to select appropriate processing conditions to avoid fruit browning during processing, storage and distribution. The PPO residual activity results are very variable, depending on the fruit/vegetable cultivar and the technology employed