Microbiological characterization of yam fermentation for ‘Elubo’ (yam flour) production

Yams (Dioscorea rotundata) were processed and fermented to the traditional West African dried yam flour Elubo. Yam slices were blanched at 60°C for 10min and then fermented at 30°C for 24h. The microbial population increased with fermentation time during the first 24h of natural fermentation with a fall in the pH from 6.2 to 5.4. The dominant aerobic mesophilic bacteria consisted of Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus delbrueckii and Bacillus subtilis. Significant contributions were also made by Lactococcus lactis, Klebsiella pneumoniae, Citrobacter freundii and the yeasts Pichia burtonii and Candida krusei. Accelerated natural lactic fermentation was achieved by repetitive use of the previous fermentation batch as an inoculum through back-slopping at a rate of 10% (w/v). After three consecutive fermentation cycles, the microflora was dominated by L. plantarum and L. brevis. Fermentation of blanched samples with pure cultures of the isolates showed L. plantarum L. brevis and B. subtilis to be the main species responsible for pH reduction and in changes in the browning levels of the reconstituted flour paste (amala). The typical colour of amala is disliked by many individuals and it seems possible that amala with a lighter colour which will be more acceptable can be produced by fermentation.     

Flavonoids and Some Other Phenolics as Substrates of Peroxidase: Physiological Significance of the Redox Reactions

2 O₂ without accumulating oxidation products of phenolics. Scavenging of H₂O₂ by the systems can proceed in vacuoles and the apoplast, because phenolics, AA and POX are normal components of the compartments. AA seems to control lignification because it reduces radicals of lignin monomers which are formed by POX-dependent reactions. On lignification, oxidation of sinapyl alcohol is enhanced by radicals of coniferyl alcohol and hydroxycinnamic acid esters when apoplastic POX rapidly oxidizes coniferyl alcohol and the esters but slowly oxidizes sinapyl alcohol. POX seems to participate in the browning of tobacco leaves and onion scales on aging. H₂O₂, which is required for the POX-dependent reactions, can be formed by autooxidation of the phenolics that are transformed to brown components. It is discussed that browning involves the formation of antimicrobial substances. Received 5 June 2000/ Accepted in revised form 1 July 2000     

Free glutamine as a major precursor of brown products and fluorophores in Maillard reaction systems

Summary. Glutamine is one of the most abundant free amino acid found in raw food. In this study, the contribution of free glutamine to nonenzymatic browning and fluorescence was investigated using an aqueous model system with methylglyoxal. The results indicated that glutamine contributed to the Maillard reaction via two pathways. First, the hydrolysis of the amide bond of glutamine led to the release of ammonia which was implicated in the formation of brown color and fluorescence. Among other nitrogen donors tested (asparagine, glutamic acid and urea) our results demonstrated that free glutamine was a major source of ammonia during heating. When heated at 120 and 180 °C, 100% of ammonia was released from glutamine after 60 and 10 min, respectively. The second pathway involved a direct Maillard reaction with the α-amino group of glutamine. Both pathways led to a rapid and complete destruction of glutamine when heated in the model systems. With reference to the Maillard browning (absorbance at 420 nm) glutamine turned out to be the most reactive amine, followed by asparagine, glutamate, ammonia and urea. Maximum fluorescence (excitation and emission wavelengths at 330 and 450 nm, respectively) was also observed with glutamine followed by urea and ammonia. Overall this study suggested that free glutamine predominantly contributes to the color and fluorescence formations of foodstuffs.     

When quinones meet amino acids: chemical, physical and biological consequences

Summary. Quinones and amino acids are usually compartmentally separated in living systems, however there are several junctions in which they meet, react and influence. It occurs mainly in wounded, cut or crushed plant material during harvest, ensiling or disintegrating cells. Diffusing polyphenols are oxidized by polyphenol oxidases (PPOs) to quinonic compounds, which associate reversibly or irreversibly with amino acids and proteins. The reaction takes place with the free nucleophilic functional groups such as sulfhydryl, amine, amide, indole and imidazole substituents. It results in imine formation, in 1,4-Michael addition via nitrogen or sulphur and in Strecker degradation forming aldehydes. The formation and activity of quinone–amino acids conjugates influences the colour, taste, and aroma of foods. Physical and physiological phenomena such as browning of foods, discoloration of plants during processing, alteration of solubility and digestibility, formation of humic substances, germicidal activity, cytotoxicity and more occur when quinones from disintegrating cells meet amino acids. The mechanisms of toxicity and the pathways by which PCBs may be activated and act as a cancer initiator include oxidation to the corresponding quinones and reaction with amino acids or peptides. Sclerotization of insect cuticle is a biochemical process involving also the reaction between quinones and amino acid derivatives.     

Glutathione and Cinnamic Acid: Natural Dietary Components Used in Preventing the Process of Browning by Inhibition of Polyphenol Oxidase in Apple Juice

Consumer demands for ‘freshness’ in processed foods has been given increasing attention by food processing industries by searching for minimally processed products. Polyphenol Oxidase (PPO) mediated browning is a major cause of undesirable flavors and nutritional losses in fruit juices. Here the anti-browning efficiency of glutathione (GSH, reduced form) and cinnamic acid (CA) in apple juice is evaluated. It was observed that the rate of the browning reaction could be efficiently delayed using GSH and CA, which act as inhibitors of PPO. Kinetic studies confirm that GSH and CA are non-competitive and competitive inhibitors of PPO respectively.     

White-to-brown transdifferentiation of omental adipocytes in patients affected by pheochromocytoma

In all mammals, white adipose tissue (WAT) and brown adipose tissue (BAT) are found together in several fat depots, forming a multi-depot organ. Adrenergic stimulation induces an increase in BAT usually referred to as “browning”. This phenomenon is important because of its potential use in curbing obesity and related disorders; thus, understanding its cellular mechanisms in humans may be useful for the development of new therapeutic strategies. Data in rodents have supported the direct transformation of white into brown adipocytes. Biopsies of pure white omental fat were collected from 12 patients affected by the catecholamine-secreting tumor pheochromocytoma (pheo-patients) and compared with biopsies from controls. Half of the omental fat samples from pheo-patients contained uncoupling protein 1 (UCP1)-immunoreactive-(ir) multilocular cells that were often arranged in a BAT-like pattern endowed with noradrenergic fibers and dense capillary network. Many UCP1-ir adipocytes showed the characteristic morphology of paucilocular cells, which we have been described as cytological marker of transdifferentiation. Electron microscopy showed increased mitochondrial density in multi- and paucilocular cells and disclosed the presence of perivascular brown adipocyte precursors. Brown fat genes, such as UCP1, PR domain containing 16 (PRDM16) and β3-adrenoreceptor, were highly expressed in the omentum of pheo-patients and in those cases without visible morphologic re-arrangement. Of note, the brown determinant PRDM16 was detected by immunohistochemistry only in nuclei of multi- and paucilocular adipocytes. Quantitative electron microscopy and immunohistochemistry for Ki67 suggest an unlikely contribution of proliferative events to the phenomenon. The data support the idea that, in adult humans, white adipocytes of pure white fat that are subjected to adrenergic stimulation are able to undergo a process of direct transformation into brown adipocytes. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.     

Browning of white adipose tissue induced by the ß3 agonist CL-316,243 after local and systemic treatment - PK-PD relationship

Transformation of white adipose tissue (WAT) to a brown adipose tissue-like (BAT-like) phenotype has emerged as an attractive approach against obesity e.g. using g ß3 adrenergic receptor agonists. These could however, produce side-effects following systemic exposure. The present study explored the possibility of local use of CL-316,243 - a selective ß3 agonist - to circumvent this problem.Rats treated s.c. for 2?weeks (0.3 and 1?mg/kg) showed decreased inguinal fat pad (IFP) weight/volume, increased UCP-1 staining and expressed BAT-like features in H&E stained micrographs. Interscapular BAT increased in weight/volume. In contrast, local treatment into the IFP was not efficacious in terms of weight/volume, despite slight increases in UCP-1 staining and changes in histological features.After local treatment, the exposure of the IFP was lower than after systemic treatment. In turn higher local doses (0.5 and 5?mg/ml) were then tested which produced a strong trend for decreased volume of the IFP, a significant increase in UCP-1 staining, and also a decrease in adipocytes size but increased number. However, after this treatment the systemic exposure was in the same range as following systemic treatment. In conclusion, we saw no evidence for the possibility of converting inguinal WAT to a BAT-phenotype solely through local activation of ß3 receptors.This is in concert with our in vitro experiments which detected direct effects of PPARγ agonists at the gene/protein expression and functional level, but were unable to detect any effect of CL-316,243.     

棕色脂肪组织与心血管疾病的关系

棕色脂肪组织 (BAT)是由棕色脂肪细胞和血管基质成分 (SVF)组成,其中SVF中包括内皮细胞、淋巴细胞、成纤维细胞以及具有多种分化功能的干细胞,在调节心血管健康与疾病上扮演着重要角色,参与心血管疾病的发生与发展。一方面,BAT通过能量代谢以及自分泌或旁分泌方式分泌的细胞因子对机体产生重要影响。BAT可以作用于心血管系统,发挥抗炎、抗心室重构等作用,从而对心血管起到保护作用。另一方面,脂肪组织来源干细胞的发现与应用,也为心血管疾病的治疗提供了有效途径。本文回顾了BAT自发现以来在人体及动物模型上的相关研究进展,论述了其与心血管损伤的相关性。     

Induction of androgenesis and callus formation inin vitro cultured anthers of a myrtaceous fruit tree (Psidium guajava L.)

Anthers ofPsidium guajava cultivated on either Murashige-Skoog's or Nitsch's basal medium (BM) or the BM supplemented with 10⁻⁶ M benzylaminopurine (BAP) were observed to contain microspores undergoing androgenic segmentations as well as a few multicellular microscopic embryoids. However, final morphogenic response from such cultured anthers was the development of calli. These calli had restricted growth accompanied by their early browning. Suspecting the browning to be due to accumulation of polyphenols, the culture medium was fortified with polyvinylpyrrolidone (PVP). PVP, increased sucrose concentration in the medium and cold pretreatment of anthers decreased the proportion of anthers turning brown as well as delayed the browning of calli, but it was not possible to maintain the calli for differentiation. Cold pretreatment significantly increased the percentage of callusing anthers and also resulted in the early emergence of calli.     

Defence response of pepper (Capsicum annuum) suspension cells to Phytophthora capsici

Cell suspension cultures of three cultivars of Capsicum annuum L., with different degrees of sensibility to the fungus Phytophthora capsici, responded to elicitation by both lyophilized mycelium and fungus filtrate. They showed conductivity changes, browning, production of the phytoalexin capsidiol and synthesis or accumulation of pathogenesis-related (PR) proteins with glucanase (EC 3.2.1.39) and chitinase (EC 3.2.1.14) activities. The cultivation medium was optimised for growth of both the plant and the fungus in order to avoid any stress during their combination. The resistant cv. Smith-5, showed a more rapid and intense response to the elicitor preparations than the sensitive cvs Americano and Yolo Wonder. This was particularly evident when the cell suspensions were elicited with the filtrate, when differences became clearly visible after only 6 h incubation. The greatest rate of capsidiol accumulation occurred after 18 h in the mycelium-elicited cells and after 12 h in those elicited with the filtrate. These times are the optimal for capsidiol accumulation, and the phytoalexin is produced much more rapidly than it can be excreted into the extracellular medium. The inhibition threshold of fungal growth (300 µg capsidiol [g dry weight]^?1) was reached only in the resistant cultivar. The induction of an intracellular glucanase (pI 8.9 and R_f 0.18) and an extracellular chitinase (pI 5.4 and R_f 0.70) only in the resistant cultivar 24 h after elicitation suggests that these enzymes are involved in the resistance to Phytophthora capsici, while other hydrolases common to all three cultivars form part of a more general defence. The results indicate that elicitation of pepper cell suspension cultures by signal molecules from P. capsici exhibits properties of a multicomponent dynamic system in which different protective mechanisms play complementary roles in the overall expression of the defence reaction. We confirm that the differential responses of resistant and susceptible pepper cultivars to P. capsici previously seen in plant stem sections are retained in suspension culture.