Identification and functional characterisation of bioactive peptides in rice bran albumin hydrolysates

The potential heath‐benefitting bioactivities of rice bran albumin hydrolysates were investigated. The antioxidant and α‐glucosidase‐ and angiotensin‐converting enzyme (ACE)‐inhibitory activities of the crude hydrolysates and their fractions were determined. The fractions with the highest bioactivities were analysed by liquid chromatography–tandem mass spectrometry/mass spectrometry to identify the active peptide sequences. Hydrolysates produced by commercial proteases Alcalase and Protamax exhibited the highest α‐glucosidase‐ and ACE‐inhibitory activities, resulting in 43.1 ± 2.1% and 54.4 ± 5.1% inhibition of the enzymes, respectively. Inhibitory activities against both enzymes were highest in the MW<3‐kDa fractions that were eluted under alkaline conditions. A number of peptide sequences were identified in the fractions, which contained several sequences with reported α‐glucosidase‐ or ACE‐inhibitory activities. This is the first time that such activities are reported for rice bran albumin hydrolysate, and it demonstrated that the hydrolysates may be developed into nutraceuticals useful in managing diabetics and hypertension.     

A proposed mechanism for the inhibition of soybean lipoxygenase by β‐carotene

The inhibition mechanism of soybean lipoxygenase (LOX) by β‐carotene was studied. Addition of β‐carotene into the reaction mixture decreased the rate of conjugated diene formation. Increasing the concentration of β‐carotene in the reaction mixture resulted in a decrease in the rate of conjugated diene formation. Although the rate of conjugated diene formation was lower in the presence of β‐carotene, the same amounts of linoleic acid hydroperoxides were formed by the enzyme at the end of the reaction, both with and without β‐carotene in the reaction medium. The rates of conjugated diene formation for 40, 20, 10 and 4 U mL^?1 LOX enzyme were almost equal to zero when the concentrations of β‐carotene were 20, 17.5, 15 and 10 µmol L^?1 in model reaction systems, respectively. β‐Carotene directly influences the amount of enzyme in the reaction medium available for the catalytic conversion of linoleic acid into corresponding hydroperoxides. The results obtained here suggest that β‐carotene reacts with linoleyl radical (L^?) at the beginning of the chain reaction, preventing the accumulation of conjugated diene forms (LOO^?, LOO^? and LOOH). Since L^? transforms back to its original form of LH, the enzyme cannot complete the chain reaction and thus remains at inactive Fe(II) form. Copyright © 2005 Society of Chemical Industry     

Inhibition of amylases present in ruminal particle‐associated micro‐organisms

The effect of different substances potentially inhibitory of ruminal amylase activity in sheep was assessed using biochemical and electrophoretic assays. Most amylase activity was detected in the particle‐associated fraction (70%) of the ruminal contents (which was selected for the assays) in comparison with the bacterial (21%) and extracellular (9%) fractions. Salts of divalent ions such as Sn²⁺, Hg²⁺, Cu²⁺ and Zn²⁺ produced 90, 82, 65 and 44% inhibition of amylase activity respectively when assayed at a relative concentration of 5 × 10^?3 mol l^?1. Organic acids such as tannic, formic, ascorbic and benzoic acid produced 79, 48, 43 and 37% inhibition respectively, whereas chelators such as EDTA, EGTA and 1,10‐phenanthroline produced an inhibition ranging from 32 to 37%. Substrate SDS‐PAGE zymograms allowed the identification of different amylase‐active bands in ruminal extracts, showing a wide range of relative molecular masses (from 36 to more than 100 kDa). Such zymograms also confirmed the effect of some inhibitors. The reversibility of the inhibitory effect of some of the assayed substances was assessed. ZnSO₄ was the most persistent inhibitory substance even at low concentrations and, owing to its low toxicity, appears to be an adequate substance to reduce the high in vitro ruminal degradation of starch. Implications for the process of enzymatic digestion of starch are discussed. © 2002 Society of Chemical Industry     

Effects of food components on the antimicrobial activity of polypropylene surfaces containing silver ions (Ag+)

The aim of this study was to investigate the influence of food components on the antimicrobial properties of surfaces containing silver. The antimicrobial activity of a polypropylene compound with a zirconium phosphate–based ceramic ion exchange resin containing silver was investigated by comparing the surface count of bacteria on sample and reference surfaces. Different food components were added to the inocula to investigate their influence on the extent of antimicrobial activity in comparison with pure inoculum (Pseudomonas fluorescens in saline solution). In the experiments with pure inoculum, a marked reduction in bacterial counts on samples containing silver was observed (7.4 log₁₀ units). However, protein‐rich food strongly reduced or completely inhibited the antimicrobial activity of silver. Almost all other tested components from the carbohydrate or lipid group did not affect the antimicrobial activity. Overall, the effect and the risks of materials containing silver needs to be analysed individually for the respective application.     

三种植物提取液的抑菌作用研究

以苦瓜、大蒜、辣椒的提取液对几种常见的食品微生物进行抑茵活性测定,结果表明,辣椒的乙醇提取液抑茵效果最好,最低抑茵浓度(MIC)为金黄色葡萄球菌1.0％,大肠杆茵1.0％,大蒜的乙醇提取液MIC值金黄色葡萄萄球茵2.1％,大肠杆茵4.2％,提取剂对苦瓜的抑茵成分的提取影响小。三者都具有热稳定性。     

Yogurt can beneficially affect blood contributors of cardiovascular health status in hypertensive rats

Cardiovascular disease is the single leading cause of death in the world and elevated blood pressure is one of the major independent risk factors. Angiotensin-I-converting enzyme-inhibitors have received considerable attention for their effectiveness in both the prevention and the treatment of hypertension. To confirm the antihypertensive effect, the influence of yogurt- and probiotic yogurt-based diets on the weight gain, serum lipid profile, and blood pressure (BP) were investigated in spontaneously hypertensive rats (14 wk old). A total of 3 dietary treatments were fed for 8 wk: skim milk diet (Feed-C), skim milk diet supplemented with freeze dried low fat yogurt (Feed-Y), and with freeze dried low-fat probiotic yogurt (Feed-PY). The total weight gain for the 8-wk period was maximum in rats fed Feed-C (90 g) followed by those fed Feed-PY (85.7 g) and Feed-Y (78.7 g), indicating that the overall weight gains were lesser (statistically non-significant) in the groups fed yogurt containing diets. At the end of the feeding period the reduction in systolic BP of rats fed Feed-Y was 3.7% (-9.5 mm Hg) and 2.7% (-6.4 mm Hg) in those fed Feed-PY while reduction in diastolic BP was 30% (-9.4 mm Hg) and 44% (-13.8 mm Hg), respectively, in comparison to those fed Feed-C. The levels of total cholesterol and low density lipoprotein-cholesterol of rats fed the supplemented diets were lower than those fed Feed-C while no changes in the levels of high density lipoprotein-cholesterol were observed. It was concluded that feeding diets supplemented with yogurts exhibited antihypertensive and hypocholesterolemic effects in spontaneously hypertensive rats.     

Antioxidant, antimicrobial, 15-LOX, and AGEs inhibitions by pineapple stem waste

Pineapple stem has been extensively used for bromelain extraction; however, almost no attention has been given to the waste obtained during bromelain manufacturing. In this regard, antioxidant, antimicrobial, and inhibitions against 15-lipoxygenase and advanced glycation end product formations by pineapple stem waste (PSW) obtained during bromelain manufacturing process were studied. The PSW had moderate bioactivities in all the performed assays. It also showed a considerable inhibition against fungal growth, probably due to high amounts of the benzoic acid present in the sample. These results indicate that PSW could be utilized as an economic source of preventive or therapeutic agent in disease and in different functional food industries. PRACTICAL APPLICATION: A large amount of wastes are generated during bromelain manufacturing from pineapple stem. So far, these wastes are not utilized and are often considered as a burden while disposing them. However, we found some important phytochemicals with considerable bioactivities in these wastes. We believe that these wastes may have a promising usage as a cheap source of one of the ingredients in functional food based industries.     

Interaction of aqueous extracts of two varieties of Yam tubers (Dioscorea spp) on some key enzymes linked to type 2 Diabetes in vitro

This study sought to assess the effect of processing of yam flour [from white yam (Dioscorea rotundata) and water yam (Dioscorea alata)] to paste, on the antioxidant properties and inhibition of key enzymes linked to type‐2 diabetes (α‐amylase and α‐glucosidase). The phenolic content (phenol and flavonoid), antioxidant properties, α‐amylase and α‐glucosidase inhibitory properties of the aqueous extracts of the yam products were determined. Processing into paste caused significant (P < 0.05) percentage decrease in their total phenol and flavonoid content of the yam varieties. However, significant increase (P < 0.05) in the antioxidant properties of the yam varieties was observed after processing. Furthermore, the yam extracts inhibited α‐amylase and α‐glucosidase activities in vitro in a dose‐dependent parttern (1–4 mg mL^?1), however, the pasting process caused significant (P < 0.05) decrease in the α‐amylase inhibitory and α‐glucosidase inhibitory activities. Therefore, processing the yam varieties into paste (browned) could potentially increase their antioxidant capacity as well as decreasing their α‐amylase and α‐glucosidase inhibitory properties.     

Effects of metal ions on formation of acrylamide and 5‐hydroxymethylfurfural in asparagine–glucose model system

Undesirable substances of thermal food processing such as acrylamide (AA) and 5‐hydroxymethylfurfural (HMF) have been intensively studied in recent decades. The aim of this work was to investigate the evolution mechanism of AA and HMF contents in the presence of various valence metal cations at various concentrations in asparagine–glucose model system. Three interesting phenomena were found. Firstly, the AA contents first decreased and then increased, whereas the HMF contents first increased and then decreased, with increasing metal cations concentration; secondly, the concentration of cations for maximal HMF contents was lower than the concentration of cations for minimal AA contents; thirdly, the maximum AA‐inhibiting or HMF‐promoting efficiency was achieved more readily with trivalent, then divalent and lastly monovalent cations. These phenomena can be explained by that increasing the metal cations concentration can increase the protonated product contents, thus increasing the AA‐inhibiting efficiency and HMF‐promoting efficiency. With higher metal cations concentration in the model system, HMF as a reactant can react with the asparagine to form AA or directly decompose into furfural. These interesting results can provide a theoretical foundation to simultaneously control the formation of AA and HMF during food processing.     

Oxidized phospholipids, isolevuglandins, and atherosclerosis

Autoxidation of polyunsaturated phosphatidylcholines (PCs) generates isolevuglandins (isoLGs) through rearrangements of isoprostanoid endoperoxides. Within seconds, isoLGs are sequestered by covalent adduction with proteins. Murine plasma isoLG-protein levels increased at least 2.5-fold in response to inflammation. IsoLG-protein adducts accumulate in vivo providing a convenient dosimeter of oxidative stress. Elevated blood isoLG-protein levels present in atherosclerosis (AS) patients point to an independent defect that is not associated with total cholesterol levels, which results in an abnormally high level of oxidative injury in AS. Protein adduction and cross-linking caused by isoLGs can obstruct protein function. For example, it interferes with proteosomal degradation of proteins and, consequently, may result in apoptotic death of smooth muscle cells and destabilization of atherosclerotic plaques. Phospholipid autoxidation also generates biologically active oxidatively truncated PCs through fragmentation of dihydroperoxydienes that can be promoted by alpha-tocopherol. The oxidatively truncated PCs in oxidized low-density lipoprotein (oxLDL) contribute to the etiology of AS by inhibiting enzymatic activities required for normal processing of oxLDL by macrophages. They promote interactions of monocytes with endothelial cells that may foster migration of monocytes into the subendothelial space. They are also ligands for unregulated receptor-mediated uptake of oxLDL by monocyte macrophages leading to foam cell formation.     

Survival of Salmonella enteritidis and changes in pH and organic acids in grated carrots inoculated or not with Lactobacillus sp and stored under different atmospheres at 4 °C

The fate of Salmonella enteritidis in grated carrots stored in air, modified atmosphere and vacuum at 4 °C was investigated with the coexistence or not of Lactobacillus sp. The population of Salmonella survived in all cases despite the presence of Lactobacillus and irrespective of the size of its inoculum. Lactic acid bacteria grew in all cases and a pH reduction was noted in all samples inoculated with Lactobacillus sp, while no such reduction occurred in sterile carrot tissue inoculated or not with S enteritidis. Sterile carrots exhibited minimum organic acid profile alterations compared to samples inoculated with Lactobacillus sp. Among these acids, lactate production was favoured under reduced oxygen conditions, in contrast to acetic acid, whose production required the presence of oxygen. These acids may act as an additional hurdle to control this pathogen under both aerobic and modified atmosphere packaging storage conditions. © 2002 Society of Chemical Industry     

Inhibition and inactivation evaluation of exogenous glycosidases in wines using p‐nitrophenylglycosides

BACKGROUND: Glycosidases are often used to improve the aroma of wines via hydrolysis of glycosidic precursors. The aim of this work was to develop a method to test activity and stability of these enzymes in wine environments using p‐nitrophenylglycosides, avoiding interference by colored substances. RESULTS: The proposed procedure for determination of glycosidase activity in wines involves quantification of the hydrolysis product p‐nitrophenol by HPLC. The method was applied to compare the inhibition of some commercial glycosidases by red and white wines. It was found that inhibition of a β‐D ‐glucosidase by ethanol, glucose and gluconolactone was smaller than that produced by wine. This enzyme was also inhibited by wine fractions rich in phenolic compounds and glycosides. When glycoside fractions were first hydrolyzed, their inhibition was strongly reduced. The stability of glycosidases in red wines was tested, showing a destabilizing effect of β‐glucosidases that was stronger than in white wine. CONCLUSION: The method developed allows measurement of glycosidase activity on p‐nitrophenylglycosides in the presence of colored wine compounds. Comparison of relative glycosidase activity in wines to that in buffer solution under the same conditions can assist in the selection of appropriate aroma‐enhancing enzymes. Copyright © 2009 Society of Chemical Industry     

Antifreeze glycoprotein agents: structural requirements for activity

Antifreeze glycoproteins (AFGPs) are considered to be the most efficient means to reduce ice damage to cell tissues since they are able to inhibit growth and crystallization of ice. The key element of antifreeze proteins is to act in a non-colligative manner which allows them to function at concentrations 300-500 times lowers than other dissolved solutes. During the past decade, AFGPs have demonstrated tremendous potential for many pharmaceutical and food applications. Presently, the only route to obtain AFGPs involves the time consuming and expensive process of isolation and purification from deep-sea polar fishes. Unfortunately, it is not amenable to mass production and commercial applications. The lack of understanding of the mechanism through which the AFGPs inhibit ice growth has also hampered the realization of industrial and biotechnological applications. Here we report the structural motifs that are essential for antifreeze activity of AFGPs, and propose a unified mechanism based on both recent studies of short alanine peptides and structure activity relationship of synthesized AFGPs.     

Changes in the carotenoid content of apricot (Prunus armeniaca,var Bergeron) during enzymatic browning: β‐carotene inhibition of chlorogenic acid degradation

Considering the numerous beneficial effects in human health ascribed to carotenoids, studies were performed to investigate the modification of carotenoid amount and composition during apricot enzymatic browning. First works on bruised apricot purees have shown a trans‐β‐carotene isomerisation (20%) induced by enzymatic browning. To clarify this isomerisation, oxidation of chlorogenic acid in presence of trans‐β‐carotene, catalysed by purified apricot polyphenoloxidase (PPO), was followed by HPLC and polarography. Isomerisation rate of trans‐β‐carotene in its cis isomer was found to increase with chlorogenic acid concentration. Moreover, trans‐β‐carotene was shown to be a potent inhibitor of phenol degradation. This inhibition was partially ascribed to PPO inhibition (non‐competitive inhibitor towards phenol with an apparent Ki close to 0.5 mM , a mixed type inhibitor towards oxygen with an apparent Ki close to 0.15 mM ). The additional inhibition was explained by non‐enzymatic reactions involving trans‐β‐carotene and chlorogenic acid o‐quinones and leading to phenol regeneration and carotene isomerisation. © 2000 Society of Chemical Industry