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'.     

Detoxification of cassava during fermentation with a mixed culture inoculum

The efficacy of a mixed culture inoculum in detoxifying intact cassava tuber and peel pieces was investigated. Fermented cassava tuber and peel pieces had more linamarase activity than the non-fermented control samples and this might have resulted partly from the release of endogenous linamarase from the retted tuber/peel pieces and partly due to the microbial linamarase. Approximately 24–26% of the total cyanide remained in the bound form in the fermented tuber while 67–79% existed as bound cyanide in the non-fermented controls. In cassava peels, only 15–33% of total cyanide remained in bound form after 72 h fermentation while 58–59% cyanide existed in bound form in the parallel non-fermented control peels. Free cyanide which could be easily eliminated through sun-drying was present at higher concentrations in the fermented tuber and peel compared with the non-fermented samples. The study showed that cassava tuber and peel could be extensively detoxified through fermentation with a mixed culture inoculum.     

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.     

木薯全粉对饼干储藏期品质和质构特性的影响

研究了木薯全粉对饼干储藏期品质和质构特性的影响,以不同比例木薯全粉替代低筋面粉制作饼干,对其理化和质构指标进行评价。结果表明:添加木薯全粉使得饼干的明亮度下降,色泽变黄。木薯全粉可降低储藏期饼干的水分含量和吸水率,提高脆性。其中,木薯全粉与低筋面粉比例为30/70时,饼干在储藏期内水分含量、咀嚼性和硬度最低,脆性最高。当木薯全粉与低筋面粉的比例大于40/60时,与对照组相比,饼干的硬度、弹性和咀嚼性升高,饼干的品质下降。     

发酵过程中韩式泡菜质构变化的研究

为加强对韩式泡菜产品质量的控制、新产品的开发,研究发酵过程中乳酸菌含量、p H、总酸度和质构物性的变化。检测发酵过程中,韩式泡菜的乳酸菌含量、p H和总酸度,用质构仪测定质构特性指标,比较不同原材料、不同发酵时间及不同部位,韩式泡菜的质构差异性。结果显示:韩式泡白菜第4 d时乳酸菌含量最大,p H为3.48,总酸度是0.51%;韩式泡胡萝卜第6 d时乳酸菌含量才达到最大值,p H为3.40,总酸度是1.26%,它们的p H比较一致,但是韩式泡胡萝卜的总酸度比韩式泡白菜的高。茎叶类和根茎类蔬菜制成的韩式泡菜,硬度、弹性、内聚性和咀嚼性等质构特性有很大差异;发酵过程中,韧性、剪切力和剪切做功等质构特性也有显著差异。在设定的实验条件下,发酵第6 d的韩式泡白菜与发酵第4 d的韩式泡胡萝卜,质构特性变化最明显。因此,茎叶类和根茎类的蔬菜原料、发酵时间的差异,都会显著影响韩式泡菜的乳酸菌含量、p H、总酸度和质构特性。      

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。     

木薯酒发酵过程中的有机酸变化及对其品质的影响分析

以新鲜甜木薯为原料,跟踪监测木薯酒发酵过程中的理化指标,并采用高效液相色谱法分析木薯酒发酵期间的有机酸组成及动态变化情况,进一步分析酒发酵过程中的酸味强度。结果表明,发酵过程中,木薯酒中的还原糖含量先快速上升至最高点最后趋于平稳（54.67 mg/mL）;酒精度先上升后平稳（7.11%vol）;总酸含量先缓慢减少至2.21 mg/mL,再缓慢增加,后快速增加,与pH值变化趋势相反。酒石酸、乳酸、乙酸、柠檬酸、琥珀酸是木薯酒发酵中重要有机酸,分别占木薯酒总有机酸含量的2.66%～12.31%,41.50%～63.53%,18.21%～23.82%,1.22%～27.77%,3.17%～15.89%,其他有机酸是酒中的辅助酸味特征成分。乳酸和乙酸是木薯酒的主体酸,其味道强度值（TAV）占总TAV值的65.82%～95.84%,发酵84 h的木薯酒有最高的味道强度值,其可达到223.87。     

朗姆酒发酵过程中微生物群落结构及其动态演替

采用高通量测序技术对朗姆酒发酵过程中的微生物群落结构及其动态演替进行研究,共检出53个细菌属和25个真菌属。结果表明,朗姆酒发酵液中细菌群落多样性始终大于真菌,且细菌群落多样性在第3天添加丹多液后达到最大,此阶段中主要优势细菌为未分类的蓝细菌属（unclassified Cyanobacteria）,第5天的细菌群落多样性最小,此阶段主要优势细菌为厚壁菌门的乳酸杆菌属（Lactobacillus）;真菌群落多样性在第2天最大,酵母菌在整个发酵过程中始终属于优势真菌;采用Mantel text分析样品中微生物群落与环境因子间的相关性,结果显示,在OUT水平上,影响细菌群落和真菌群落多样性的主要是pH值,且真菌群落多样性与pH之间具有显著正相关（P＜0.05）。     

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...     

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。     

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。     

酱香型白酒第二轮次酒发酵过程微生物多样性研究

为探究酱香型白酒二轮次发酵过程中微生物群落结构的变化、微生物多样性以及物种与样品之间的关系,应用高通量测序技术对酱香型白酒第二轮次酒生产堆积及窖池发酵过程酒醅中微生物的多样性及其主要功能菌群进行研究。结果表明,在堆积过程中共检测到细菌138个属,真菌54个属;窖池发酵过程中共检测到细菌262个属,真菌267个属。酒醅中主要细菌类群为Firmicutes和Proteobacteria,主要真菌类群为Ascomycota和Basidiomycota。堆积过程中绝对优势细菌属有Bacillus、Enterococcus、Lactococcus、Lactobacillus;绝对优势真菌属有Thermoascus、Thermomyces、Candida、Aspergillus。在窖池发酵酒醅中其绝对优势细菌属为Lactobacillus;绝对优势真菌属为Saccharomyces、Candida、Penicillium、Fusarium。由于堆积、窖池发酵酒醅所处发酵环境、发酵物料物态及其工艺参数差异较大原因,使得两者之间生物物种存在较大差异。     

木薯全粉对蛋糕品质及其质构特性的影响

以不同比例木薯全粉替代低筋面粉制作蛋糕,研究木薯全粉对蛋糕物理特性、感官品质和质构特性的影响,对其品质和质构指标进行评价。结果表明:随着木薯全粉替代比例的增加,蛋糕回缩率先降后升,感官总分先升后降,烘焙损失率、密度、硬度和咀嚼性不断升高,比容、水分含量、弹性和内聚性不断降低;替代比例为10/90~30/70的蛋糕回缩率、烘焙损失率、密度均比对照低,水分含量比对照高,有利于蛋糕品质的提升;替代比例为30/70的蛋糕比容、感官总分、硬度、咀嚼性和内聚性与对照差异不显著;替代比例超过40/60后,与对照组相比,蛋糕回缩率、烘焙损失率、硬度和咀嚼性显著升高(P0.05),比容、感官总分、水分含量、弹性和内聚性显著降低(P0.05),蛋糕品质下降。     

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.     

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。     

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.     

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.