Inhibition of apple polyphenol oxidase activity by sodium chlorite

Synergistic inhibition of Pseudomonas fluorescens growth and proteases activities via sodium chlorite-based oxyhalogen

Pseudomonas fluorescens is considered among the main spoilage microorganisms due to its ability to produce proteases. Food deterioration caused by spoilage microorganisms has a major impact on food quality and the environment. The inactivation of Pseudomonas fluorescens growth and protease production was intensively investigated with the use of Salmide®, A Sodium Chlorite-Based Oxy-halogen Disinfectant. A unique M9 media was also developed to assure sufficient protease productions with different mutants of Pseudomonas fluorescens as a microbioreactor. Mutations were induced by classical whole-cell mutagenesis using N-methyl-N'- nitro-N-nitrosoguanidine (NTG). A dramatic decrease occurred in protease activity when different Salmide concentrations (5, 10, and 15 ppm) were added to the growth culture followed by a complete inhibition concentration (20, 25, 50, and 100 ppm) of Salmide. However, no significant inhibition occurred once it is secreted out of cells. Some mutants were resistant and remains highly stable with high protease production under stressful conditions of Sodium Chlorite-Based Oxy-halogen. The production of the protease showed a linear correlation with the increase in incubation time using a continuous culture bioreactor system and recorded maximum protease activity after 40 h. Our findings would offer alternative antimicrobial procedures for food and industrial sectors.

Application of sodium chloride and quince seed gum pretreatments to prevent enzymatic browning, loss of texture and antioxidant activity of freeze dried pear slices

ABSTRACT

In the study the effect of sodium chloride and quince seed gum solutions as immersion pretreatment to prevent enzymatic browning reaction in pear slices before freeze drying was evaluated. Four levels of gum concentrations (0%, 0.25%, 0.5% and 1%) and three concentrations of salt (0%, 0.25% and 0.5%) were used. Subsequently, freeze drying method was used to dry the pear slices and the qualitative, structural and sensory characteristics of dried pear slices were investigated. The moisture content of the dried pear slices decreased significantly with increasing sodium chloride concentration, while increasing the concentration of the gum significantly increased the moisture content (P < 0.05). Use of both immersion pretreatments were effective in maintaining the antioxidant activity and reducing browning index of the slides and with increasing concentration of the immersion solutions, the antioxidant activity loss decreased in the slices (P < 0.05). Electron microscopy study revealed that the microstructural changes of the drying process on the slices are very slight, although gum pre-treatment at the high levels made a layer on the surface of the pear slices which slowed down the transfer of water vapor molecules. By considering the results of qualitative, structural and sensory evaluations, using of immersion pretreatment with 0.25% gum and 0.25% salt solution to prevent enzymatic browning along with preserving the quality properties of pear slices prior to the drying process is recommended.

GRAPHIC ABSTRACT

SEM of cross section of dried pear slices after processing.

Synergistic Effect of NaCl Pretreatment and PVP on Browning Suppression and Callus Induction from Petal Explants of Paeonia Lactiflora Pall. 'Festival Maxima'

Browning is prevalent in tissue cultures of Paeonia lactiflora Pall. (herbaceous peony), and severely affects and restricts the growth and differentiation of the explants. In this study, dipping excised explants in a sodium chloride (NaCl) solution as a pretreatment, adding polyvinyl pyrrolidone (PVP) to the culture medium, storing planted explants at 4 °C for 24 h, and transferring planted explants to a new medium after 24 h were considered as browning-suppression methods in tissue cultures of herbaceous peony 'Festival Maxima'. The treated petal explants were cultured in a culture room with a 16-hour photoperiod, 25 °C temperature, and 80% relative humidity in darkness for 4 to 8 weeks. The results demonstrated that dipping excised explants in a 0.5 g·L-1 NaCl solution, adding 0.5 g·L-1 PVP to the medium, storing planted explants at 4 °C for 24 h, and transferring planted explants to the same fresh medium after 24 h could effectively inhibit browning. Adding PVP to the medium led to the greatest browning suppression percentage of 95%. Storing planted explants at 4 °C for 24 h reduced the effectiveness of other treatments in suppressing browning. After 8 weeks, dipping excised explants in a NaCl solution resulted in the highest callus induction percentage of 75%, while storing explants at 4 °C for 24 h suppressed callus formation. It was observed in all treatments that decreases in browning was accompanied with higher levels of phenols and lower activities of phenylalanine ammonia-lyase (PAL) and polyphenoloxidase (PPO). Overall, the results suggest that dipping in a NaCl solution was effective in alleviating the browning issues of herbaceous peony tissue cultures, and had positive synergistic effects with PVP on browning suppression and callus induction.

Browning in apples: Exploring the biochemical basis of an easily-observable phenotype

Many fruits and vegetables undergo browning when they are cut and the tissue is exposed to the air. This is due to the activity of the enzyme polyphenol oxidase (PPO, EC 1.14.18.1) with endogenous substrates. In this laboratory experiment, students prepare slices of different varieties of apples and assess the rate of browning. They make a simple extract of the apple tissue and measure the activity of PPO using 3,4-dihydroxy-l-phenylalanine (l-DOPA) as substrate. They determine the protein concentration of the extract with the Bradford Coomassie Blue reagent and calculate the specific activity of PPO. Finally, the students measure the total concentration of the potential substrates for PPO with the Folin-Ciocalteau phenol reagent using a gallic acid standard curve. By comparing the tendency of the apples to turn brown, the specific activity of PPO, and the concentration of potential substrates, they can assess the biochemical basis of the browning phenotype. This experiment can be done as a series of weekly laboratory exercises, as an intensive 1-week laboratory project, or as the basis of an extended student research investigation. © 2017 by The International Union of Biochemistry and Molecular Biology, 46(1):76-82, 2018.

Deodorization of Garlic Breath by Foods, and the Role of Polyphenol Oxidase and Phenolic Compounds

Garlic causes a strong garlic breath that may persist for almost a day. Therefore, it is important to study deodorization techniques for garlic breath. The volatiles responsible for garlic breath include diallyl disulfide, allyl mercaptan, allyl methyl disulfide, and allyl methyl sulfide. After eating garlic, water (control), raw, juiced or heated apple, raw or heated lettuce, raw or juiced mint leaves, or green tea were consumed immediately. The levels of the garlic volatiles on the breath were analyzed from 1 to 60 min by selected ion flow tube mass spectrometry (SIFT-MS). Garlic was also blended with water (control), polyphenol oxidase (PPO), rosemarinic acid, quercetin or catechin, and the volatiles in the headspace analyzed from 3 to 40 min by SIFT-MS. Raw apple, raw lettuce, and mint leaves significantly decreased all of the garlic breath volatiles in vivo. The proposed mechanism is enzymatic deodorization where volatiles react with phenolic compounds. Apple juice and mint juice also had a deodorizing effect on most of the garlic volatiles but were generally not as effective as the raw food, probably because the juice had enzymatic activity but the phenolic compounds had already polymerized. Both heated apple and heated lettuce produced a significant reduction of diallyl disulfide and allyl mercaptan. The presence of phenolic compounds that react with the volatile compounds even in the absence of enzymes is the most likely mechanism. Green tea had no deodorizing effect on the garlic volatile compounds. Rosmarinic acid, catechin, quercetin, and PPO significantly decreased all garlic breath volatiles in vitro. Rosmarinic acid was the most effective at deodorization.

Discoloration of indigo carmine using aqueous extracts from vegetables and vegetable residues as enzyme sources

Several vegetables and vegetable residues were used as sources of enzymes capable to discolor indigo carmine (IC), completely or partially. Complete discoloration was achieved with aqueous extracts of green pea seeds and peels of green pea, cucumber, and kohlrabi, as well as spring onion leaves. The source of polyphenol oxidase (PPO), pH, time, and aeration is fundamental for the discoloration process catalyzed by PPO. The PPO present in the aqueous extract of green pea seeds was able to degrade 3,000 ppm of IC at a pH of 7.6 and magnetic stirring at 1,800 rpm in about 36 h. In addition, at 1,800 rpm and a pH of 7.6, this extract discolored 300 ppm of IC in 1:40 h; in the presence of 10% NaCl, the discoloration was complete in 5:50 h, whereas it was completed in 4:30 h with 5% NaCl and 2% laundry soap.