Souring and breakdown of cyanogenic glucosides during the processing of cassava into akyeke

The population and composition of the lactic acid bacteria microbiota as well as the content of cyanogenic glucosides occurring at various stages of fermentation and subsequent processing of cassava roots into akyeke, a steamed sour cassava meal, were investigated. The number of lactic acid bacteria and percentage titratable acidity increased during 5 days of fermentation, but decreases were observed in the subsequent operations of 'washing' the dough with water followed by partial drying and steaming. In field and laboratory samples, Lactobacillus plantarum accounted for 59.3% and 52.3%, Lactobacillus brevis 23.3% and 22.8% and Leuconostoc mesenteroides subsp. cremoris 14.5% and 15.8%, respectively, of all lactic acid bacteria isolated at various stages of fermentation and processing. A reduction of about 98% occurred in the total cyanogens (CN) content of cassava roots during processing, from 69.3 to 1.4 and 110.3 to 2.8 mg CN equivalent/kg dry weight for laboratory and field samples of akyeke, respectively.     

Effects of processing of grated cassava roots by the 'screw press' and by traditional fermentation methods on the cyanide content of gari

The extent of the loss of hydrocyanic acid (HCN) from grated cassava roots, selected from both the sweet and bitter varieties, was compared in the roasted grit (gari) derived from their fresh pulp which had been dewatered and fermented by two different processes; the quick (1-day) 'screw press' method (QSP) and the slow (3-day) traditional one (STD), respectively. The relative amounts of HCN which had disappeared after 1 day, in the case of QSP, and 3 days, in respect of STD, were comparable (92–100%) for either free (non-glycosidic) or bound (glycosidic) cyanide content of the two cultivars, indicating that the former method was more efficient than the latter in the detoxification of the grated pulp. The QSP method appeared to retain some of the bound cyanide while with the STD method, virtually no bound cyanide was detectable. About 83–91% of the total HCN content of the grated roots was present as free cyanide. It would seem that varietal differences in HCN contents of cassava may not be a critical factor in the preferential selection of the roots for 'garification'.     

Starch and pectin solubilization and texture modification during pre-cooking and cooking of cassava root (Manihot esculenta Crantz)

Physico-chemical alterations of cell-wall constituents and of substances stored in the cell characterize the behavior of fresh vegetables during cooking. Pre-cooking for 1 h at three different temperatures was used to identify alterations in hydration, pectin and starch solubilization and the relation to texture determination by a compression and a shear test. Samples of cassava (Catarina amarela) harvested 8 months after planting date were used. Soluble galacturonic acid in the treatment water varied from 0.07 to 0.2.1 mg/100 ml while soluble solids varied from 271.3 to 599.6 mg/100 ml. Soluble starch varied from 114.3 to 437.7 mg/100 ml and total solids varied from 292.4 to 611.4 mg/100 ml during pre-cooking from 55 to 75 °C. There was weight reduction of 4 and 2 g/100 g of material and reduction of compression force in the treatments at 55 and 65 °C in relation to the raw sample and weight gain of 6.7 g/100 g and increase in compression force at 75 °C. Shear force decreased from the raw sample to the 65 °C treated sample while pectin solubility increased up to 75 °C. Samples cooked in boiling water had weight gain of 6.8 g/100 g of material, 493.3 mg/100 ml of soluble solids and 588 mg/ 100 ml of total solids of which 507.6 mg was starch.     

Microbial community dynamics during the Scamorza Altamurana cheese natural fermentation

The growth dynamics of the natural microbial community responsible for the fermentation of Scamorza Altamurana, a typical Southern Italian cheese made using backslopping, was investigated applying a polyphasic approach combining 1) microbial enumeration with culture media, 2) randomly amplified polymorphic DNA (RAPD) fingerprinting of microbial communities, 3) sequencing of partial 16S ribosomal DNA (rDNA) genes, and 4) physiological tests. Viable cell counts on different culture media showed that the cocci community prevailed during the 18 h of curd fermentation and the 6 d of cheese ripening. RAPD fingerprinting made it possible to isolate 25 different strains identified by 16S rDNA sequencing as belonging to five species of Lactobacillus, three species of Streptococcus, one species of Weissella, and one species of Enterococcus. The physiological analyses of all lactic acid bacteria strains revealed that the isolates belonging to Streptococcus genus were the most acidifying, whereas lactobacilli were most proteolytic. Streptococcus thermophilus C48W and Lactobacillus delbrueckii subsp. bulgaricus B15Z dominated all through the fermentation process. Furthermore, they seemed to be stable in a subsequent whey sample analyzed after 7 mo. The recovery of strains endowed with interesting technological features, such as acidifying and proteolytic activities, and surviving in natural whey could allow the upscaling of cheese processing safeguarding the organoleptic characteristics of Scamorza Altamurana and could possibly improve other fermented dairy products.     

豆酱自然发酵过程中质地变化及相关性分析

采用质地多面分析法(TPA)对东北传统豆酱自然发酵过程中硬度,黏着性,内聚性和胶着性的变化情况进行探讨,分析了测定参数的变化与感官评价指标间的相关性,结果表明,随着发酵时间的延长,黏着性和内聚性呈上升趋势,硬度和胶着性呈先上升后下降趋势。黏着性和内聚性与感官评价指标间呈极显著正相关关系。以仪器测定参数硬度、黏着性、内聚性和胶着性为变量建立感官评定预测模型,结果表明,黏着性和内聚性对感官评价指标影响较大。     

酸菜自然发酵过程中的质地变化

以自然发酵酸菜为研究对象,应用质构仪质地多面分析(Texture Profile Analysis,TPA)法对自然发酵过程中酸菜质地变化进行分析,探讨了质构仪各项参数之间的相关性及自然发酵过程中各参数的变化规律。结果表明,大多数的质构参数之间呈现显著相关性,酸菜的硬度1、脆度、回复性、凝聚性及咀嚼性随着发酵时间的延长整体呈现下降的趋势,且发酵40～60 d时是食用酸菜品质最佳的时期。     

宣恩火腿发酵过程中表面微生物群落演替规律

为揭示宣恩火腿发酵过程中微生物群落演替规律,运用高通量测序技术分析不同发酵时间火腿表面细菌和真菌群落组成,并对物种相关性和微生物群落功能进行分析.结果表明:宣恩火腿表面细菌群落多样性在发酵过程中持续增加,共检出11个门和96个属;发酵前、中期,木糖葡萄球菌(Staphylococcus xylosus)占绝对优势(>9...     

中国传统食醋微生物污染及控制措施研究进展

食醋微生物污染是导致食醋腐败变质的最主要原因,有效地检测和控制污染微生物是保证食醋安全以及进一步发展的基础。该文对食醋污染微生物的原因、危害以及种类进行了综述,开放式发酵环境及容器管道的不洁是食醋污染微生物的主要原因,致使胀气、产膜、发黏及浑浊等现象发生,最终造成企业经济损失并对消费者健康造成隐患。总结了目前的检测方法和控制措施,现有的传统微生物培养检测方法弊端很多,非培养技术更能满足快速准确的检测要求。除加热和添加防腐剂等常用控制措施外,紫外线消毒、膜过滤等技术也逐渐应用。针对现有研究的不足,展望了食醋污染微生物未来的研究方向,以期为食醋污染微生物的深入研究及有效控制提供参考和理论依据。     

用木薯液化滤液对木薯粉调浆进行浓醪酒精发酵工艺研究

研究用木薯液化滤液对木薯粉调浆进行浓醪酒精发酵的工艺条件。主要利用α-淀粉酶对木薯浆进行液化、过滤处理,重点考察液化时固液比、保温时间、pH值、酶用量等因素对木薯粉液化得率的影响。再用液化滤液对木薯粉调浆进行浓醪酒精发酵试验,考察发酵醪液在整个发酵过程中物料流动性能及发酵效果。结果表明木薯浆液化的固液比为1∶11,pH值为6.2,在90℃以上保温75min,液化酶用量为15U/g。在此工艺条件下木薯粉液化固形物得率为85.10%。使用不同比例液化液对木薯粉调浆至初始总糖为25.5%(w/v)进行浓醪酒精发酵,发酵醪酒精度均达15.0%vol以上。结论:利用木薯液化滤液对木薯粉调浆进行浓醪酒精发酵,发酵醪在发酵过程的流动性增加50%,能够顺利进行浓醪酒精发酵。     

Effect of Rhizopus fermentation on the lipid composition of cassava flour

Studies were made on the complex lipid and fatty acid compositions of commercial cassava flour before and after nutritional ‘upgrading’ with Rhizopus arrhizus. The flour lipids closely resemble those found in other plant tissues except for a lower content of polyunsaturated acids and a higher content of free fatty acid. This can be accounted for by degradation during processing. Rhizopus fermentation leads to the appearance of γ-linolenic acid and changes in the percentage of other acids. The total lipid content falls and the typical plant glycolipids disappear to be replaced by mould phospholipids. Sterol glycoside present in the original flour is not metabolised and becomes a major component of the final material.     

Factors in the protein enrichment of cassava by solid state fermentation

The enrichment of cassava protein content using solid substrate fermentation was studied on both laboratory and on-farm scales using Aspergillus niger as a starter. The effects of cassava particle size and of various nitrogen source ratios and mixing methods were investigated. Ammonium sulphate and urea as sources at respective levels of addition (g N kg⁻¹ substrate) of 10:10, 20:10 and 20:20 were used in combination with cassava alone and cassava mixed with rice bran and soya bean each having mixing levels of 50, 100 and 150 g kg⁻¹. The mixture was fermented for 84 h at 35°C and 90–95% RH on the laboratory scale and 29–31°C and 95–99% RH at the on-farm scale. The results indicated that cube sizes ranging from 0.3 to 0.5 cm³ gave good mycelial growth. Pure cassava alone at the 10:10 nitrogen addition level produced the highest protein yield of about 145 g kg⁻¹. The on-farm technique yielded higher protein enrichment compared with laboratory experiments. Cassava alone yielded 230 g kg⁻¹ protein while cassava with rice bran and cassava with soya bean each produced 210 g kg⁻¹ protein.     

不同处理方式下毛竹笋发酵过程中质地变化分析

为了评价发酵对毛竹笋食用品质的影响,研究了不同处理方式下毛竹笋在发酵过程中其质构、微观结构和色泽的变化。结果表明:不同处理方式下,毛竹笋的硬度、脆性、凝聚性等质构特性显著下降,不同发酵方式对硬度、脆性、凝聚性等影响较大,而对弹性和回复性的影响不明显;4种处理方式中,以漂烫乳酸菌发酵竹笋保鲜效果最好,以该法保藏63 d之后,毛竹笋硬度、脆性、凝聚性、咀嚼性、弹性和回复性分别为:67.87 N,77.68 N,0.302,6.61 N,0.345,0.511,损失相对较小;通过扫描电镜观察竹笋的微观结构发现,毛竹笋在发酵之后,其薄壁细胞组织出现明显的皱缩,细胞间隙增加;其中漂烫乳酸菌发酵竹笋样品细胞结构保持较为完整;经过不同处理以后,毛竹笋色泽变化较明显,总色差ΔE2,其中漂烫乳酸菌发酵竹笋样品色差最小为8.71,具有较好的护色效果;综合评价发现,漂烫乳酸菌发酵较其他3种方式更能有效保持毛竹笋的质构特性,护色效果最佳。     

Microbial transglutaminase-mediated modification of ovalbumin

In the present paper we have investigated the impact of microbial transglutaminase on thermally treated ovalbumin. In fact, ovalbumin was modified by microbial transglutaminase following heat treatment for 1 h at 80 °C. The protein was both intra- and inter-molecularly crosslinked as shown by the formation of high molecular weight polymers and a monomer having similar molecular weight but higher electrophoretic mobility when compared to unmodified ovalbumin. Analysis of simulated digestion under physiological conditions has demonstrated that the biopolymers obtained after transglutaminase treatment were more resistant to both gastric and duodenal digestion. Whilst they started gradually being digested after 5 min of incubation with pepsin, some of them were still present even after 60 min incubation with the duodenal enzymes, trypsin and chymotrypsin. Furthermore, incubation of 1.5% (w/v) ovalbumin gel in the presence of transglutaminase led to the formation of a well-developed viscoelastic gel network with higher modulus and lower phase angle values. These results suggest a possible use of transglutaminase-modified ovalbumin in the food industry as a potential ingredient to enhance both the functional properties of many food-based products, such as digestibility, and mechanical properties, such as viscoelasticity and gel strength.     

Microbial population dynamics during spontaneous fermentation of Asparagus officinalis L. young sprouts

The aim of the present study was to assess the spontaneous fermentation of Asparagus officinalis L. young sprouts. For this purpose, asparagus fermentation was performed according to a traditional procedure originating from northern Greece. Young asparagus sprouts were cut, submerged in a brine solution (8 % NaCl) and placed in room temperature for fermentation to occur. Fermentation was monitored by measuring pH and total titratable acidity values as well as by qualitative and quantitative assessment of the microbiota dynamics. The latter was performed by classical microbiological techniques; clustering was performed by SDS-PAGE of whole cell proteins and rep-PCR and identification by sequencing of the 16S-rRNA gene. A culture-independent approach [PCR-denaturing gradient gel electrophoresis (DGGE)] was also applied in order to obtain a more integrated view of the microbiota dynamics. Lactic acid bacteria prevailed the fermentation forming a microbial consortium that was stable at species level; Lactobacillus sakei and Enterococcus faecium dominated until the 5th day while Weissella viridescens and W. cibaria dominated from the 7th day until the end of fermentation. Combination of SDS-PAGE with rep-PCR resulted in a very efficient clustering and differentiation also at sub-species level, revealing a succession at that level of all species throughout fermentation. On the other hand, application of PCR-DGGE was of limited usefulness.     

Changes in some chemical constituents during the fermentation of cassava tubers (Manihot esculenta, Crantz)

Cassava tuber, Manihot esculenta, Crantz, was processed, after five days of fermentation, into ‘gari’ and ‘lafun’. The pH fell from 6·5 to 4·3 in the former. Titratable acidity increased during the course of fermentation. No cyanide residue was detected in gari by fluorimetry although low cyanide levels were detected in some samples of lafun. Thin layer chromatography (TLC) of extracts from gari confirmed the absence of cyanogenetic glycosides.     

微生物发酵法生产食品风味物质

微生物发酵法已经成为生产食品风味物质的一种重要手段.主要对食品中的常见的芳香风味物质(主要包括醛类、酮类、酯类、萜类等)和味感风味物质的微生物发酵进行了概述,并介绍了几种用于生产风味物质的发酵方式.     

微生物发酵竹香鸡加工技术

研究了利用微生物发酵技术,添加益生菌生长促进剂加工竹香鸡的加工工艺和技术要点。     

量热法监控生物发酵过程的研究

量热法是生物热化学的重要方法之一,适合于生物体系各个层次的研究。在生物反应器的发酵过程中,量热法作为一种新的技术,简单适用,有着很大的市场前景。本文主要通过对生物发酵过程中罐体热流变化的研究,得出热量控制对生物发酵的影响,从而为大规模生产发酵过程的在线控制提供一定指导意义。     

酪蛋白水解物对酸奶发酵的促进作用及其对酸奶质构的影响

将酪蛋白水解物(含蛋白质7.6%)以2%(w/w)添加到奶液中混合发酵,做空白样对照。研究了二者发酵过程中各发酵参数的变化,并对二者的质构进行了分析比较。研究结果表明,酪蛋白水解物能明显促进酸奶发酵;促发酵作用随所添加的水解物水解程度提高而增强;添加酪蛋白水解物改变了酸奶发酵过程中的pH下降速度:添加样在发酵前半期的pH下降速度高于空白样,而发酵后半期空白样的pH下降速度略快;发酵中期,二者的pH下降速度存在最大差距;质构分析表明,添加2%酪蛋白水解物对酸奶整体质构有明显改善。     

Microbial succession and metabolite changes during fermentation of saeu-jeot: Traditional Korean salted seafood

Saeu-jeot is made by the fermentation of highly salted [approximately 25% (w/v)] shrimp in Korea. Saeu-jeot samples were prepared in triplicate and their cell number, bacterial community, and metabolites were monitored periodically for 183 days. Quantitative PCR showed that bacterial populations were much more abundant than archaeal populations during the entire saeu-jeot fermentation period, which suggested that bacterial populations, not archaeal populations, might be primarily responsible for saeu-jeot fermentation. Pyrosequencing analysis revealed that Proteobacteria were dramatically replaced with halophilic Firmicutes as the fermentation progressed and members of Pseudoalteromonas, Staphylococcus, Salimicrobium, and Alkalibacillus were sequentially dominant and, eventually, Halanaerobium predominated after 66 days of fermentation. Halophilic archaeal genera, Halorubrum, Halolamina, Halobacterium, Haloarcula, and Haloplanus belonging to Euryarchaeota, were dominant, but their communities were relatively constant over the entire fermentation period. Metabolite analysis using a ¹H NMR spectroscopy showed that the amount of metabolites including amino acids, glycerol, and nitrogen compounds rapidly increased during the early fermentation stage, but their levels were relatively constant or they decreased after approximately 49 days of fermentation. A statistical analysis based on bacterial communities and metabolites demonstrated that members of Halanaerobium might be responsible for the production of acetate, butyrate, and methylamines after 66 days of fermentation, which could be considered as a potential indicator to decide the appropriate seafood fermentation time. This study will provide insights into the microbial succession and metabolites of fermented seafood and allow for a greater understanding of the relationships between the microbial community and metabolites in seafood fermentation.