Degradation of Lycopene and β‐carotene in Model Systems and in Lyophilized Guava during Ambient Storage: Kinetics,Structure, and Matrix Effects

ABSTRACT: Being highly unsaturated, carotenoids are susceptible to isomerization and oxidation during the processing and storage of food. In the present study, the degradation of acyclic lycopene and dicyclic β‐carotene in low‐moisture and aqueous model systems, as well as in lyophilized guava, during storage at ambient temperature, in the absence or presence of light, was investigated. Both carotenoids followed first order kinetics under the various conditions investigated. Lycopene degraded much faster than β‐carotene in all the model systems. In a comparison of lycopene isolated from guava, tomato, and watermelon, greater losses were observed with lycopene from tomato. Since the model system was identical in the 3 cases, these results indicated that other compounds from the food sources, co‐extracted with lycopene, might have influenced the oxidation. Light consistently and strongly promoted degradation under all conditions studied. The susceptibility of lycopene to degradation was much less in lyophilized guava than in the model systems, showing the marked protective influence of the food matrix. Loss of β‐carotene, found at a concentration of about 18 times lower than lycopene, was only slightly lower than that of lycopene in lyophilized guava, indicating that the effect of matrix and/or the initial concentration overshadowed the structural influence.     

Inhibition of Aldose Reductase Activity by Extracts from Hops

The inhibitory effect of beer on aldose reductase was investigated. Components present in beer strongly inhibited aldose reductase. Inhibition activity was observed primarily in the methanol‐soluble fraction of the beer and active components were identified to be of hop origin. Further, a component was identified as iso‐α‐acids, which are well known as main bitter components of beer. The inhibition rate of iso‐α‐acids was similar to quercetin, which is known to be a strong inhibitor of aldose reductase activity.     

Purification and immunolocalization of the peroxisomal 3-oxoacyl-coA thiolase from Saccharomyces cerevisiae

A molecular understanding of peroxisome biogenesis depends upon the analysis of peroxisomal proteins. Here we describe the isolation of the 3-oxoacyl-CoA thiolase of the peroxisomal β-oxidation system from Saccharomyces cerevisiae as a dimer of identical subunits, each with a molecular mass of 45 kDa. Monospecific polyclonal antibodies were raised against the purified enzyme, and its peroxisomal origin was demonstrated by immunoblotting of subcellular fractions as well as by immunogold labelling. We also show that these antibodies could be suitable for an immunofluorescence microscopy screening of yeast mutants affected in peroxisome assembly.     

Effects of Heat Treatment on the Carotenoid and Tocopherol Composition of Tomato

Abstract: The objective of this study was to determine the influence of thermal processing on the assessment of tocopherols and carotenoids, as well as their isomer formation in tomatoes. The sliced tomatoes were heated in an oven at 100, 130, and 160 °C for 5, 10, and 20 min, then freeze‐dried. Freeze‐dried samples were finely ground and the analysis was performed on lyophilized samples. The average concentrations of total lycopene, lutein, β‐carotene, α‐tocopherol, and γ‐tocopherol in fresh tomatoes (in 100 g dry weight) were 21.2, 1.1, 2.7, 8.0, and 2.5 mg, respectively. Oven baking of tomato at 160 °C for 20 min led to a significant increase in the apparent measurement of lycopene, β‐carotene, and α‐tocopherol content by 75%, 81%, and 32%, respectively. Heating induced isomerization of (all‐E) to various (Z) isomers of lycopene, and we found that the total (Z)‐lycopene proportion in the tomatoes increased with longer heating time. (All‐E)‐lycopene constituted 75.4% in fresh tomatoes and decreased to 52.5% in oven‐baked tomatoes (160 °C, 20 min), while (5Z)‐lycopene increased from 9.4% to 17.9% of total lycopene. However, β‐carotene release and isomerization was less influenced by the heat treatment than that of lycopene. These results suggested that thermal processes might break down cell walls and enhance the release of carotenoids and tocopherols from the matrix, as well as increase isomerization of lycopene and β‐carotene.     

Excessive membrane development following exposure of the methylotrophic yeast Hansenula polymorpha to oleic acid-containing media

We studied the physiological responses of Hansenula polymorpha during adaptation of cells to oleic acid-containing media. Growth experiments indicated that the organism was unable to use oleic acid as the sole source of carbon and energy. However, upon incubation of glucose-grown cells in mineral media containing oleic acid, activities of various enzymes of the β-oxidation pathway were induced. These enzymes were localized in microbodies together with alcohol oxidase. Furthermore, a drastic increase in phospholipid content of the cells was observed; this was due to a rapid proliferation of membranes. These consisted of a variable number of membranous layers which were continuous with the peroxisomal membrane. Upon continued incubation, the membrane proliferations extended and large compartments were formed. This process was dependent on the presence of peroxisomes in the cells since it was not observed in peroxisome-deficient mutant strains of H. polymorpha. The newly formed membranous compartments differed from peroxisomes since they did not contain peroxisomal matrix proteins; these were confined to the single enlarged organelle which was incorporated in the membranous structure and characterized by a large alcohol oxidase crystalloid. The membranous compartments are considered to be whole entities since they could not be separated from the peroxisomes by common cell fraction methods; also they were degraded entirely after a shift of cells to glucose-excess condition. Freeze fracturing reveled that the substructure of the membranes greatly resembled that of normal peroxisomal membranes. Since a distinct enhancement of different peroxisomal membrane proteins was observed during the initial hours after the shift, we assume that exposure of H. polymorpha to acid lead to a drastic overproduction of peroxisomal membranes.     

Effects of Pulses of Higher Temperature on the Development of Enzyme Activity During Malting

The increase of temperature at the beginning, in the middle and at the end of malting has been evaluated in terms of quality parameters (malting losses, index of acrospire development, friability, HWE, viscosity, SNR) and enzyme (β‐glucanase and α‐amylase) development, in a good quality malting barley (Otis) and a higher protein‐higher β‐glucan content barley used for feed (Extra). A shift from 15 to 20°C at the beginning of malting was shown to increase acrospire development, friability, HWE and SNR and to reduce viscosity, without significantly affecting malting losses. This effect was related to higher β‐glucanase and α‐amylase activities within each variety. However, the same enzyme activities were not directly related to a better malting quality when the two genotypes were compared. This confirms previous indications that diversity in malting performance between genotypes cannot simply be traced back to differences in enzyme activities; but, indeed, it suggests that, for a defined barley lot, changes in the levels of enzyme activities following different malting procedures may have a direct effect on malt quality.     

Melatonin improves survival and respiratory activity of yeast cells challenged by alpha‐synuclein and menadione

One of the hallmarks of Parkinson disease is α‐synuclein aggregate deposition that leads to endoplasmic reticulum stress, Golgi fragmentation and impaired energy metabolism with consequent redox imbalance. In the last decade, many studies have used Saccharomyces cerevisiae as a model in order to explore the intracellular consequences of α‐synuclein overexpression. In this study we propose to evaluate the respiratory outcome of yeast cells expressing α‐synuclein. Cell viability or growth on selective media for respiratory activity was mainly affected in the α‐synuclein‐expressing cells if they were also treated with menadione, which stimulates reactive oxygen species production. We also tested whether melatonin, a natural antioxidant, would counteract the deleterious effects of α‐synuclein and menadione. In fact, melatonin addition improved the respiratory growth of α‐synuclein/menadione‐challenged cells, presented a general improvement in the enzymatic activity of the respiratory complexes and finally elevated the rate of mitophagy, an important cellular process necessary for the clearance of damaged mitochondria. Altogether, our data confirms that α‐synuclein impairs respiration in yeast, which can be rescued by melatonin addition.     

Hydrolysis of β-glucosyl ester linkage of p-hydroxybenzoyl β- -glucose, a chemically synthesized glucoside, by β-glucosidases

To investigate the hydrolysis of glucosyl esters by β-glucosidase, p-hydroxybenzoyl β- -glucose (pHBG) was chemically synthesized. The hydrolytic activity of some β-glucosidases for pHBG was compared to that for p-nitrophenyl β-glucoside (pNPG). The Clavibacter michiganense and Flavobacterium johnsonae enzymes could hydrolyze pHBG and steviol glycosides which are natural glucosyl esters. The commercial β-glucosidase originating from Caldocellum saccharolyticum also hydrolyzes pHBG despite having no activity for steviol glycosides. The β-glucosidase from Aspergillus niger cleaved the glucosyl ester linkage much more weakly than the glucosidic linkage. The pH-activity profile for the hydrolysis of pHBG was similar to that of pNPG by the C. saccharolyticum β-glucosidase. The similar profiles for these substrates suggested that the active site for the glucosyl ester chemically resembles that for glucoside with respect to catalysis. Kinetic analysis of the C. saccharolyticum β-glucosidase for mixed substrates of pHBG and pNPG showed that the hydrolysis of pHBG competed with that of pNPG. This result indicated that there is only one active site for both the glucosyl ester and glucoside. Mass spectroscopic analysis of the hydrolysates of pHBG in H₂¹⁸O suggested that β-glucosidase hydrolyzes glucosyl esters between the anomeric carbon of glucose and the carbonyl oxygen, not between the carbonyl carbon and the carbonyl oxygen.     

A Simulation Model for the Control of beta‐Glucanase Activity and beta‐Glucan Degradation During Germination in Malting

A dynamic model was developed that describes the formation of β‐glucanase and the degradation of β‐glucans at different temperatures and grain moistures during the germination of malting barley. The process was analysed by simulations and by solving an optimal control problem for maximising the β‐glucanase activity. The results demonstrate the effects of controlling dynamically the germination process and improve the understanding of cytolysis in germination.     

COMPARATIVE STUDIES OF THE β-D-GLUCAN RELEASED INTO SORGHUM AND BARLEY WORTS

Worts prepared from two cultivars of Nigerian grown sorghum six day melts — LI87 end SK5912 had β-D-glucan levels off five to seven times more than that of proctor barley. In contrast to barley, malting of the sorghums results in the release off more β-D-glucan into wort. Apparently, this is due to increasing levels of β-glucan solubilase and (1→3)-β-glucanase during malting with no significant (1→3, 1→4)-β-glucanase activity.     

Tomatine,chlorophyll, β‐carotene and lycopene content in tomatoes during growth and maturation

Tomato (Lycopersicon esculentum) plants synthesise nutrients, pigments and secondary metabolites. These include the green pigment chlorophyll, the yellow pigment β‐carotene, the red pigment lycopene and the colourless glycoalkaloid α‐tomatine. The levels of these compounds are strongly influenced by the maturity of the tomatoes. Widely consumed Japanese tomato varieties Momotaro, Momotaro‐T93 and First Memory at five different stages of ripeness, each harvested at 10, 20, 30, 40 and 50 days after flowering of the plants, were analysed for the contents of these compounds. Additionally, tomato clusters from different locations along the vine on the same plant were also evaluated. The results show that chlorophyll and tomatine concentrations decrease rapidly during the growth of the tomatoes. By contrast, β‐carotene and lycopene levels are low in immature and high in mature tomatoes. The location of the tomato clusters and tomato variety did not significantly affect these results. The possible usefulness of these results to optimise health‐promoting effects of tomatoes is discussed. © 2003 Society of Chemical Industry     

THE INSTITUTE OF BREWING ANALYSIS COMMITTEE THE DETERMINATION OF ENDO-β-GLUCANASE ACTIVITY IN MALT

Various substrates for the determination of malt endo-β-glucanase activity have been tested in conjunction with the β-glucanase procedure advocated by Bourne and Pierce. It is recommended that one universal standard substrate should be used and that each determination should be measured against a standard check malt. Furthermore, great care must be exercised in the dissolution of the substrate to obtain consistent results.     

AN APPROACH TO THE IDENTIFICATION OF A ß-GLUCAN SOLUBILASE FROM BARLEY1

A ß-glucan solubilase activity was demonstrated in barley extract. This enzyme catalyzed the dissolution of barley ß-glucan by releasing a product having a narrow molecular weight distribution and a molecular weight of about 20,000. The enzyme was partially purified by ion exchange chromatography on DEAE-cellulose and gel permeation chromatography on Bio-Gel P-100. Although carboxypeptidase activity was present in the crude extract of barley flour the partially purified ß-glucan solubilase did not hydrolyse N-CBZ-Phe-ala. Examination of extracts from different barley tissues indicated that the ß-glucan solubilase activity was associated with the husks only; a large portion of the activity was extractable from whole barley kernels. About 85% of the enzyme activity in crude extracts from barley flour was retained after 40 min at 62°C. However, the enzyme was much more heat-labile in extracts of whole barley kernels. The pH of maximal activity was found to be about pH 5.7 and results from column chromatography suggested that the enzyme had a low pl value and a MW between 5 × 10⁴ and 6 × 10⁴.     

Gac fruit (Momordica cochinchinensis Spreng.): a rich source of bioactive compounds and its potential health benefits

Gac (Momordica cochinchinensis Spreng.) is a tropical vine originating from South and South‐East Asia. Gac fruit has traditionally been used in Asia to provide red colour for cuisines and enhance visional health. Recently, Gac fruit has emerged as a potential source of carotenoids, especially lycopene and β‐carotene. Carotenoids and other identified bioactives from this fruit including phenolics, flavonoids and trypsin inhibitors are associated with many beneficial bioactivities such as antioxidant, anticancer and provitamin A activities. In addition to the traditional utilisation, commercial products like Gac powder and Gac oil have been manufactured as natural colourants and medicinal supplements. This paper is a review of the scientific literature on the nutritional composition, biological activities and processing of Gac fruit.