大曲贮存过程中原核微生物群落结构及风味成分演替规律

【目的】研究大曲贮存过程中原核微生物群落结构及风味成分变化规律,阐述大曲贮存阶段的必要性和重要性,并探索不同微生物种属之间的相互关系,为更好地控制大曲品质提供微生物和风味方面的参考依据。【方法】通过Mi Seq高通量测序剖析大曲成熟过程中原核微生物群落结构变化;利用共存(Co-occurrence)模式方法分析不同种属微生物之间的相关关系,预测其相关性;利用SPME-GC-MS分析贮存过程中大曲风味成分的变化规律。【结果】采用Mi Seq测序方法共得到3 710个OTUs,除不能有效比对的序列外共鉴定出29个门和160个种属。其中,乳杆菌属、芽孢杆菌属、明串珠菌属、高温放线菌属、乳球菌属等是大曲中的优势菌群。随大曲贮存时间推移,贮存前期不断积累酸、醇类物质,后期酯类及含氮类等重要风味物质不断形成,而4-甲基苯酚等异味物质的含量却不断降低。相关性分析结果表明,乳酸菌与乳酸、乙酸等酸类物质之间存在显著的相关性,芽孢杆菌与酸类及含氮化合物之间存在显著的相关性。【结论】大曲贮存过程中,原核微生物结构不断发生调整,风味物质向更优质白酒风味进行变化。除环境因素外,原核微生物的代谢活动对风味物质的形成具有重要的影响,因此大曲贮存是白酒酿造过程中必不可少的环节。     

Net effect of wort osmotic pressure on fermentation course, yeast vitality, beer flavor, and haze

The net effect of increased wort osmolarity on fermentation time, bottom yeast vitality and sedimentation, beer flavor compounds, and haze was determined in fermentations with 12° all-malt wort supplemented with sorbitol to reach osmolarity equal to 16° and 20°. Three pitchings were performed in 12°/12°/12°, 16°/16°/12°, and 20°/20°/12° worts. Fermentations in 16° and 20° worts decreased yeast vitality measured as acidification power (AP) by a maximum of 10%, lowered yeast proliferation, and increased fermentation time. Repitching aggravated these effects. The 3rd “back to normal” pitching into 12° wort restored the yeast AP and reproductive abilities while the extended fermentation time remained. Yeast sedimentation in 16° and 20° worts was delayed but increased about two times at fermentation end relative to that in 12° wort. Third “back-to-normal” pitching abolished the delay in sedimentation and reduced its extent, which became nearly equal in all variants. Beer brewed at increased osmolarity was characterized by increased levels of diacetyl and pentanedione and lower levels of dimethylsulfide and acetaldehyde. Esters and higher alcohols displayed small variations irrespective of wort osmolarity or repitching. Increased wort osmolarity had no appreciable effect on the haze of green beer and accelerated beer clarification during maturation. In all variants, chill haze increased with repitching.     

Flavoring and extending the shelf life of cucumber juice with aroma compounds-rich herbal extracts at 4 °C through controlling chemical and microbial fluctuations

This work aims to enhance the flavor of functional cucumber juice using herbal extracts of peppermint, basil, lavender, and lemongrass ethanolic extracts and extend its lifetime by controlling the chemical and microbial fluctuations. Cucumber juices were processed as; non-supplemented (J-Con), J-PME, J-BE, J-LE, and J-LEE supplemented with peppermint, basil, lavender, and lemongrass ethanolic extracts, respectively. Peppermint extract was significantly scavenged 88% of DPPH radicals and inhibited the growth of tested gram-positive, gram-negative bacteria and fungi followed by the lemongrass extract. The antioxidant activity of cucumber juices increased due to polyphenols and aroma compounds in the added extracts. However, the antioxidant content was decreased after two months of storage at 4 °C, due to the decrease in polyphenols. The flavor compounds were determined using GC mass, wherein hydrocarbons, acids, alcohols, and carbonyl compounds were the main aroma contents in cucumber juices, and their contents decreased with storage time. Peppermint and lemongrass extracts were significantly (p ≤ 0.05) increased the whiteness of J-PME, and J-LEE, respectively. The highest score of flavor and taste was observed in J-PME that scored 8.3 based on panelists'' reports followed by J-LEE. The PME was significantly maintained 91% of the odor and color of J-PME as compared to other juices.     

Volatile components of whole and different plant parts of bastard balm (Melittis melissophyllum L., Lamiaceae) collected in Central Italy and Slovakia

The aim of this work was to trap the volatiles released from whole frozen and dry aerial parts, and, separately, from different organs (leaves, stems, corolla and calyx) of bastard balm (Melittis melissophyllum L., Lamiaceae) populations collected in Italy and Slovakia by HS-SPME, and to identify the headspace constituents responsible for the characteristic aroma impression by GC/FID and GC/MS techniques. Among more than 100 volatile components detected, the C(8) alcohol oct-1-en-3-ol, responsible for the typical mushroom-like odor, and the phenolic coumarin, with a characteristic sweet and creamy vanilla bean odor, played a major role in the aroma of whole aerial parts and different plant organ samples. In particular, dry calyx parts could be proposed as flavoring agent in food products as mushroom aroma enhancer. Multivariate chemometric techniques, such as cluster analysis and principal component analysis, were used to characterize the sample populations according to the geographical origin and processing of plant material.     

Retronasal perception of odors

Odors often produce different sensations when presented in front of the nose or intraorally, when eaten. It is a long-standing question whether these differences in sensations are due, for example, to the additional mechanical sensations elicited by the food in the mouth or additional odor release during mastication. To study this phenomenon in detail, a stimulation technique has been developed that allows controlled ortho- or retronasal presentation of odorous stimuli. Results from psychophysical, electrophysiological, and imaging studies suggest that there are clear differences in the perception of ortho- and retronasal stimuli. This 'duality of the sense of smell' is also observed in a clinical context where some patients exhibit good retronasal olfactory function with little or no orthonasal function left, and vice versa. The differences between ortho- and retronasal perception of odors are thought to be, at least partly, due to absorption of odors to the olfactory epithelium, which appears to differ in relation to the direction of the airflow across the olfactory epithelium.     

Characterization of an enriched lipoxygenase extract from Aspergillus niger in terms of specificity and nature of flavor precursors production

Aspergillus niger was grown for 6 days, and the harvested biomass was homogenized; the resultant supernatant, considered as the crude enzymatic extract, was enriched by ammonium sulfate precipitation. The extract was assayed for its lipoxygenase (LOX) activity using a wide range of polyunsaturated fatty acids (PUFAs), including linoleic, linolenic and arachidonic acids, as substrates. Two pH maxima were determined at 5.0, 10.5. The K_m and V_max values indicated that the microbial LOX displayed preferential substrate specificity towards linolenic acid at low pH. The microbial LOX demonstrated preferential substrate specificity towards free fatty acids over the acyl esters of linoleic acid. It was shown that the LOX activity of A. niger produced all monohydroperoxy regioisomers of the PUFAs, and there was a predominance of conjugated diene hydroperoxides. Significant production of the unconjugated 10-hydroperoxides of both linoleic and linolenic acids was obtained by the LOX activity. The amounts of 10-hydroperoxides ranged from 15 to 21% of total produced isomers, for linolenic and linoleic acids, respectively. The greatest proportion of the 10-regioisomer was attributed to the maximum activity at pH 5.0. Four major hydroperoxy-eicosatetraenoic acid (HPETE) regioisomers were isolated from the bioconversion of arachidonic acid, including the 8-, 9-, 12- and 15-HPETE, which accounted for approximately 97% of total isomers.     

采用代谢组学分析技术分析工业啤酒发酵过程中风味物质生成规律

啤酒风味是保证啤酒品质的关键因素之一。运用代谢组学的方法,分析工业啤酒发酵过程中酵母胞内代谢物和啤酒风味物质的对应关系,从代谢水平上研究风味物质形成过程中的关键影响因素。在啤酒发酵过程中,同时检测风味物质的含量变化和酵母胞内代谢物的变化,对得到海量的、多维的代谢数据采用主成分分析（PCA）和偏最小二乘分析（PLS）的多元统计分析方法进行处理。由PCA分析结果可知：磷酸、海藻糖、琥珀酸、谷氨酸、天冬氨酸、丙氨酸对主成分贡献比较大,说明这些代谢物在不同发酵阶段含量变化显著。由PLS分析结果可知：对啤酒风味影响最大的物质主要为氨基酸,包括丝氨酸、缬氨酸、苏氨酸、赖氨酸、丙氨酸、亮氨酸和天冬酰胺等,这为啤酒中风味物质的调控提供了一定的理论指导。     

Sol-gel powders and supported sol-gel polymers for immobilization of lipase in ester synthesis

Candida rugosa lipase was entrapped in hybrid organic–inorganic sol-gel powder prepared by acid-catalyzed polymerization of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes, and used in catalyzing esterification reactions between ethanol and butyric acid in hexane. Optimum preparation conditions were studied, which are gels made from propyltrimethoxysilane (PTMS)/TMOS molar ratio=4:1, hydrolysis time of silane precursor=30 min, water/silane molar ratio=24, enzyme loading=6.25% (w/w) of gel, and 1 mg PVA/mg lipase. The percentage of protein immobilization was 95% and the resulting lipase specific activity was 59 times higher than that of a non-immobilized lyophilized lipase. To prepare magnetic lipase-immobilized sol-gel powder (MLSP) for easier recovery of the biocatalyst, Fe₃O₄ nanoparticles were prepared and co-entrapped with lipase during gel formation. This procedure induced surface morphological change of the sol-gel powder and showed adverse effect on enzyme activity. Hence, although only 9% decrease in protein immobilization efficiency was observed, the corresponding reduction in enzyme activity could be up to 45% when sol-gel powder was doped with 25% (v/v) Fe₃O₄ magnetic nanoparticles solution. Lipase-immobilized sol-gel polymer was also formed within the pores of different porous supports to improve its mechanical stability. Non-woven fabric, with a medium pore size of all the supports tested, was found to be the best support for this purpose. The thermal stability of lipase increased 55-fold upon entrapment in sol-gel materials. The half-lives of all forms of sol-gel-immobilized lipase were 4 months at 40 °C in hexane.     

中国悬钩子属植物的利用价值概述

主要报道中国悬钩子属植物作为果树种质资源和药用植物的利用价值及果实色素和香味成分的利用潜力。经过十余年的调查１引种栽培和观测评价,发现一些种类可以作为野生小果类果树直接利用,其中２３种４变种是悬钩子类果树选育种的优良种质。据文献记载和民间调查发现。４５种４变种悬钩子植物可以作为中草药治疗多种疾病。对灰白毛莓、高梁泡、蓬、掌叶复盆子和黑莓果实色素的研究结果表明：悬钩子果实色素以醇提法为佳,水提法效果     

A single-host fermentation process for the production of flavor lactones from non-hydroxylated fatty acids

Lactone flavors with fruity, milky, coconut, and other aromas are widely used in the food and fragrance industries. Lactones are produced by chemical synthesis or by biotransformation of plant-sourced hydroxy fatty acids. We established a novel method to produce flavor lactones from abundant non-hydroxylated fatty acids using yeast cell factories. Oleaginous yeast Yarrowia lipolytica was engineered to perform hydroxylation of fatty acids and chain-shortening via β-oxidation to preferentially twelve or ten carbons. The strains could produce γ-dodecalactone from oleic acid and δ-decalactone from linoleic acid. Through metabolic engineering, the titer was improved 4-fold, and the final strain produced 282 mg/L γ-dodecalactone in a fed-batch bioreactor. The study paves the way for the production of lactones by fermentation of abundant fatty feedstocks.