Pročišćavanje i karakterizacija polifenolne oksidaze, peroksidaze i lipoksigenaze iz svježe salate (L. sativa)

Enzymatic reactions taking place in minimally processed vegetables are considered as a major problem, because they adversely affect sensorial and nutritional quality. Polyphenol oxidase (PPO), peroxidase (POD) and lipoxygenase (LOX) from lettuce were purified on a column packed with positively charged diethylaminoethyl (DEAE) cellulose by applying pH gradient elution from pH=4.0 to 9.0. The main purified fractions (PPO1 and PPO4, POD1 and POD2, LOX1 and LOX2) were characterized for enzyme concentration-reaction rate relationship, thermal stability, pH activity and kinetic parameters. Kinetic properties of each isoform were considerably different. Cysteine was found as the most effective inhibitor of both fractions of PPO. Kinetic parameters of lettuce POD were presented using guaiacol at various H2O2 concentrations. β-carotene directly influences lettuce LOX in the reaction medium available for the catalytic conversion of linoleic acid into hydroperoxides. Ascorbic and oxalic acids appear as effective PPO inhibitors, protecting phenolic compounds against oxidation in lettuce. Understanding the characteristics of deteriorative enzymes becomes important to maintain suitable conditions for fresh-like quality of lettuce. The results can be useful to keep the nutritional quality of minimally processed lettuce during shelf-life.Enzimske reakcije što se odvijaju u minimalno obrađenom povrću veliki su problem, jer nepovoljno utječu na njihova senzorska i hranjiva svojstva. Polifenolna oksidaza (PPO), peroksidaza (POX) i lipoksigenaza (LOX) izdvojene su iz salate i pročišćene eluacijom pomoću gradijenta pH (s pH=4,0 na pH=9,0) na koloni napunjenoj pozitivno nabijenom dietilaminoetil celulozom. Ispitane su ove značajke glavnih pročišćenih frakcija (PPO1 i PPO4, POD1 i POD2, te LOX1 i LOX2): odnos koncentracije enzima i brzine reakcije, toplinska stabilnost, optimalna pH-vrijednost za aktivnost enzima, te kinetička svojstva, koja se znatno razlikuju za svaki izo-oblik. Cistein je najučinkovitije inhibirao obje frakcije polifenolne oksidaze. Kinetičke su značajke peroksidaza iz salate ispitane pomoću gvajakola i različitih koncentracija vodikova peroksida. Na aktivnost lipoksigenaze izravno je utjecao β­-karoten pri pretvorbi linolne kiseline u hidroperokside. Askorbinska i oksalna kiselina učinkovito su inhibirale polifenolnu oksidazu i tako sprečavale oksidaciju fenolnih spojeva u salati. Radi održavanja odgovarajućih uvjeta čuvanja svježe salate važno je razumijeti osobine enzima koji uzrokuju njezino propadanje. Dobiveni su rezultati korisni pri određivanju uvjeta skladištenja minimalno obrađene salate radi očuvanja njezinih hranjivih svojstava

Antiglycative effect of fruit and vegetable seed extracts: Inhibition of AGE formation and carbonyl-trapping abilities

BACKGROUND: Advanced glycation end-products (AGEs) are the final products derived from the non-enzymatic glycation process. AGEs are involved in the development of several health complications associated with diabetes and aging. Searching for anti- AGE extracts is necessary to mitigate the effects of age-related pathologies. RESULTS: The antioxidant and antiglycative activities of eight aqueous extracts of fruit and vegetable seeds were evaluated. All seed extracts (3.6 mg mL-1) exhibited anti-AGE activity in protein-glucose assay, ranging from 20 to 92% inhibition compared with aminoguanidine (4.87 mmol L-1). Green pepper extract exerted the highest anti-AGE activity. However, peach and pomegranate extracts exhibited the highest anti-AGE activity in protein-methylglyoxal assay, ranging from 0 to 79% inhibition. Hazelnut, almond and sesame extracts were not effective when methylglyoxal was the promoter. Apricot and peach extracts appeared to inhibit the formation of AGEs through their capacity for direct trapping of 1,2-dicarbonyls (IC50=0.14 mg mL-1). No relationship between antioxidant and phenolic compound content and antiglycative activity was found. Therefore other hydrophilic constituents in addition to phenolic acids must be involved in the antiglycative activity of the extracts. CONCLUSION: Aqueous extracts of fruits and vegetables can be considered in the prevention of glycation-associated complications of age-related pathologies. © 2012 Society of Chemical Industry.Peer Reviewe

Alkali-based pre-treatment may prevent ochratoxin A in grapes

In traditional raisin production process in Turkey, one of the major raisin producers in the world, grapes undergo an alkali treatment prior to drying. This procedure involves dipping grapes in a potassium carbonate solution for 10-15 seconds to remove the wax layer on the surface to accelerate the drying process. In this study, we aimed to investigate the effect of alkali treatment on ochratoxin A (OTA), an important risk factor for grapes and grape-derived products. First, the stability of the OTA was examined under variable pH (4-12), ion type (Na+, K+), ionic strength (0.1-10%) and temperature (4-60 degrees C). Then, Aspergillus ochraceus contaminated grapes were treated with an alkaline solution and a subsequent OTA analysis was performed through a high performance liquid chromatography-fluorescence detection. OTA started to decompose at pH values exceeding 10.0. The degradation followed a first order kinetics. Although both sodium carbonate and potassium carbonate solutions were at the same alkali pH and they both triggered the OTA degradation at increasing concentrations, potassium carbonate was more effective even at low concentrations. Elevated temperatures were also found to effect degradation. The degradation rate constant at 40 degrees C was approximately 5 times greater than the one at 25 degrees C. Furthermore, OTA levels dropped up to 50% in contaminated grapes after the alkali treatment. Our results confirmed that the amide bond of OTA rapidly hydrolysed to a non-toxic ochratoxin-alpha and phenylalanine under strong alkaline conditions. The results suggest that the alkaline pre-treatment unintentionally offers a great advantage to reduce OTA levels in raisins and it could be a viable approach for other dried fruits through the application of good manufacturing practice