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.     

双波长分光光度法测定木薯块根淀粉含量的动态变化

以双波长分光光度法测定SC201、SC205、GR891和GR911共4个木薯品种生育期块根中直链淀粉与支链淀粉含量的动态变化.结果表明,4个木薯品种块根直链淀粉的含量是随生育期的延长而逐渐增加的,而支链淀粉的含量却缓慢下降,支链淀粉/直链淀粉的比例呈现下降趋势,到12月份4个品种的这一比例已接近相同;以鲜重计的总淀粉含量,4个品种均呈逐渐增加的趋势;而以干重计的总淀粉含量的变化则4个品种表现不一致.研究初步揭示了木薯块根直链淀粉、支链淀粉和总淀粉含量的积累规律.     

Evaluation of substrates and storage conditions for preparing and maintaining starter cultures for tempeh fermentation.

Heat-pasteurized cassava root, cowpeas, partially defatted peanuts, rice and soybeans were evaluated for their suitability to support growth and sporulation of the tempeh mold, Rhizopus microsporus var. oligosporus, and the oncom mold, Neurospora intermedia, at 25, 30 and 37 degrees C. The molds grew best and sporulated most luxuriantly on cassava and rice incubated at 37 degrees C. Viability of molds remained high for up to 30 weeks when dried (a(w) 0.48), powdered substrates on which the molds had been cultured, were stored at 5, 25 and 37 degrees C. Survival was best when powders were stored at 5 degrees C, although storage at 25 degrees C did not cause a marked decline in CFU/g. R. microsporus var. oligosporus starter cultures produced on rice and then stored for 20 weeks at these temperatures compared most favorably with commercial starter cultures for preparing high-quality soybean tempeh. The simple technology required to prepare these starter cultures enhances the potential for their application in developing countries where the introduction of nontraditional fermented legume foods to low-protein diets could help to ameliorate malnutrition.     

Effect of processing methods on quality and acceptability of fufu from low cyanide cassava

The effects of steeping whole and grated tubers and of periodic change of water during steeping on the quality and acceptability of fufu from low-cyanide cassava were evaluated. Steeping increased the acidity and reduced the pH and cyanide content of cassava. Grating the tuber before steeping improved aroma, and periodical change of water during steeping improved taste, colour and texture of fufu over that produced by the traditional method. Fufu from low-cyanide cassava had an acceptability similar to that of fufu from high-cyanide cassava. However, oven drying of the flour significantly reduced acceptability of fufu.     

Hydrolysis of Tropical Tuber Starches by Bacterial and Pancreatic α-Amylases

Action of porcine pancreatic and Bacillus subtilis α-amylases on native tuber starches of yam (Dioscorea alata), sweet potato (Ipomea batatas) and tannia (Xanthosoma sagittifolium) was studied in comparison with the well known potato and cassava starches. Large differences in enzymes susceptibilities were observed when studied on 24h. Yam starch was 3.5% hydrolysed with 2,8 μkat amylase/g starch, three times less than potato and tannia starches while sweet potato starch was 53% hydrolysed, two times less than cassava starch. Except yam, level of hydrolysis was higher with porcine pancreatic amylase than with the Bacillus subtilis amylase while initial hydrolysis rate was lesser. Microscopic observations and image analysis pointed out that the polyhedric shaped granules of tannia, sweet potato and cassava starches were much more damaged than the spherical ones. Pitting occured preferentially on the edges of the granules and the enzymes penetrated into the starch granule by pores and canals of corrosion. Conversely to other starches, hydrolysis of yam starches evidenced greater differences between action of Bacillus subtilis and pancreatic α-amylases. The enzymes acted by pitting some parts of the granules surface, the number of pores and their size being related to enzyme source.     

The use of a starter culture in the fermentation of cassava for the production of "kivunde", a traditional Tanzanian food product

Three cassava fermentation methods (spontaneous fermentation, back-slopping and the use of starter culture) for the production of kivunde, executed in three trials at 30 degrees C, were compared in terms of cyanide level reduction, microbiology and product quality improvement. Among the isolates from spontaneously fermented cassava batches, four strains were selected on the basis of their enzymatic activities and acid production. All were identified as Lactobacillus plantarum and were used as starters in this study. Lowest residual cyanide levels were detected after 120 h fermentation time in samples fermented with the starter culture and were below the maximum value of 10 mg/kg recommended by the Codex/FAO for cassava flour. This finding seems to be related to the alpha-glucosidase activity of the inoculated strains of which API-zyme (Bio-Merieux) tests showed activities of between 20 and > or = 40 nmol/4 h. The total residual cyanide levels of the spontaneous and back-slopping fermentations at 96 h were respectively 43.5 and 47.7 mg/kg dry weight of cassava. Extension of the fermentation period to 5 days, lead to further substantial reduction in the residual cyanide level in both these processes, but not below the recommended maximum value as in the case of starter culture fermented products. The spontaneous and back-slopping fermented cassava showed signs of deterioration after 3 days of fermentation. There was a sharp drop of pH and an increase of titratable acidity for all three batches during the first 48 h followed by a slow rise of pH and drop in titratable acidity towards the end of fermentation. The samples fermented with the starter culture had a smooth texture and pleasant fruity aroma, as opposed to the course and dull appearance and more complex flavour of the samples of spontaneous and back-slopping batches. During fermentation with starter culture, Enterobacteriaceae and yeasts and moulds could not be isolated throughout the period of fermentation (detection limit: 10 colony forming units/g). The present findings indicate the suitability of these Lb. plantarum strains as starter cultures for cassava fermentation in the kivunde process. The paper highlights the potential for the improvement of a traditional African fermented food (kivunde) through the use of a starter culture.     

An evaluation of enzymic and autolytic assays for cyanide in cassava (Manihot esculenta,crantz)

The total cyanide contents of cassava parenchymal tissue (peeled roots), cassava cortex (peel) and cassava leaves were evaluated by autolytic and enzymic assays. Autolysis of parenchymal tissue was studied under different conditions of _pH, time and temperature and addition of exogenous enzyme and antibiotic. Optimal conditions were determined to be 24 h at 37°C in acetate buffer (0.1M ; _pH 5.5) with 0.1 mg ml^?1 chloramphenicol. Total cyanide contents similar (about 90%) to those obtained by enzymic assay could be achieved only by the use of small sample sizes: < 1 g of parenchymal tissue, < 0.3 g of cortex and < 0.1 g of leaf tissue. This caused sampling problems because of the presence of cyanide gradients in cassava tissues, which could only be resolved by tissue homogenisation prior to analysis. A study using the enzymic assay of cyanide stability in such homogenates, at different _pH values and temperatures, has indicated that subsampling must be done within 15 min so as to prevent appreciable losses in the measured cyanide contents. The rate of loss of total cyanide was found to depend not only on the proportion of total cyanide which is non-glucosidic (free), but also on the proportion of the non-glucosidic cyanide present as cyanohydrins. The implications with regard to residual cyanide contents on cassava processing and the advantages of the enzymic assay over autolytic methods are discussed.     

PROCESSING TECHNIQUES AND HYDROCYANIC ACID CONTENT OF CASSAVA-BASED HUMAN FOODSTUFFS IN NIGERIA

The hydrocyanic acid content of peeled cassava tubers from various localities in Eastern Nigeria (major cassava growing and consuming area) varied from 26 ± 1.6 to 38 ± 2.6 mg/100g fresh weight. There was no correlation between the cyanide contents of cassava tubers and locality. Processing the tubers with the highest cyanide content into different forms of cassava-based foodstuffs (i.e. Garri, Fufu, cassava cake and cassava chips for cassava salad) consumed in Nigeria resulted in an undetectable amount of cyanide. It is concluded that these cassava-based foodstuffs consumed in Nigeria are free from cyanide toxication, and the incidence of ataxic neuropathy associated with prolonged consumption of cassava as a result of its cyanide content should not be due to prolonged consumption of processed cassava products.     

Some Enzyme Properties of Raw Starch Digesting Amylases from Streptomyces sp. No. 4

Streptomyces sp. No. 4 produce two forms of amylase that attack raw cassava starch. Both forms, amylase‐1 and amylase‐2, were purified by starch adsorption, affinity chromatography, and ion exchange chromatography. The molecular weights of amylase‐1 and amylase‐2 as determined by SDS‐PAGE were 56 kD and 77 kD, respectively. Optimal enzyme activities occurred at pH 5.5 and at 50°C for amylase‐1 and at 45°C for amylase‐2. The activation energy of amylase‐1 and amylase‐2 were 67 and 42 kJ/mol, respectively. Hg²⁺ and pCMB inhibited both enzymes, whereas 2‐mercaptoethanol activated only amylase‐2. EDTA inhibited amylase‐1 but activated amylase‐2. The main product of hydrolysis of raw cassava starch by amylase‐1 was maltose, followed by maltotriose, maltotetraose and dextrin. Amylase‐2 cleaved raw cassava starch to produce glucose and maltose as main products. Both amylase‐1 and amylase‐2 are α‐amylases, as shown by the fast disappearance of iodine staining, the corresponding reaction products and the ability of both enzymes to hydrolyze crosslinked blue starch.     

Combinations of antimycotics to inhibit the growth of molds capable of producing 1,3-pentadiene

Some species of molds are capable of degrading sorbic acid to produce 1,3-pentadiene, a volatile compound with an unpleasant hydrocarbon-like odor. The effectiveness of reduced concentrations of sorbate, in combination with other antimycotics, to control the growth of these molds has not been described. We did a study to evaluate potassium sorbate, sodium benzoate, calcium propionate, disodium ethylenediaminetetraacetic acid (EDTA), and natamycin, alone and in combination, for their effectiveness in preventing the growth of five molds isolated from Parmesan cheese and a lemon-flavored drink subjectively judged to contain 1,3-pentadiene. Growth of Penicillium brevicompactum, Penicillium roqueforti, Paecilomyces variotii, Aspergillus niger, and Cephaloascus fragrans on model agar media containing Parmesan cheese (PRM agar) (pH 5.5) and lemon-flavored drink (LD agar) (pH 2.6) supplemented with antimycotics was studied. All molds grew well at 21 degrees C on PRM agar containing potassium sorbate (3500microg/ml), calcium propionate (3000microg/ml), or natamycin (20microg/ml). Combinations of potassium sorbate (250-1000microg/ml), calcium propionate (250-1000microg/ml), and/or natamycin (10-18microg/ml) greatly inhibited or prevented growth of molds on PRM agar, indicating their potential as preservative systems at pH values resulting in large percentages of the acids in dissociated forms. Three of the five molds grew on LD agar containing potassium sorbate or sodium benzoate at a concentration of 200microg/ml. Growth did not occur within 70 days on LD agar containing EDTA (30microg/ml) in combination with potassium sorbate and sodium benzoate at 50 and 175microg/ml, respectively, or 175 and 50microg/ml, respectively. Results of this study show that preservative systems containing a reduced concentration of potassium sorbate, in combination with other antimycotics, particularly natamycin, have potential for controlling the growth of molds thought to be capable of producing 1,3-pentadiene.     

短波紫外线处理对木薯保鲜效果及生理指标的影响

探讨短波紫外线对木薯果实感官品质、营养品质和生理指标的影响,为木薯的贮运保鲜提供技术指导。以‘华南5号’木薯果实为试材,以波长254 nm紫外线杀菌灯为辐射源,比较研究不同时间的紫外线处理对木薯品质的影响。结果表明：与对照相比,紫外线处理能够显著推迟果实硬度的下降和色泽的转变,延缓总可溶性固形物（TSS）含量的增加和淀粉的降解,并且能够抑制丙二醛（MDA）的积累,维持超氧化物歧化酶（SOD）和过氧化物酶（POD）活性在较高的水平,保持果实的贮藏品质,推迟果实的成熟软化过程。综合来看,30 min紫外线处理时间对木薯品质的保持最好,20 min处理次之,10 min效果最差。     

马克斯克鲁维酵母木薯乙醇发酵工艺研究

通过单因素试验对一株耐高温马克斯克鲁维酵母（Kluyveromyces marxianus）HY32的木薯乙醇发酵工艺进行了研究。结果表明,HY32利用木薯发酵乙醇的最佳工艺条件为料水比1∶5（g∶mL）,发酵时间96 h,接种量11%,发酵温度40 ℃,液化时间1 h,液化温度95 ℃,液化酶添加量为20 U/g淀粉,糖化酶添加量为150 U/g淀粉,硫酸铵添加量6 g/L,初始pH=5.0。在此条件下,HY32发酵木薯酒精度可达8.90%vol,淀粉利用率与淀粉出酒率分别为87.120%和49.48%,残糖量为0.03 g/L。与未优化的初始发酵条件相比,发酵醪的酒精度提高了16.65%。     

用于微生物油脂发酵的木薯淀粉水解工艺的优化

为了提高木薯淀粉的发酵产脂能力,采用正交实验和均匀设计法对木薯淀粉酶法水解工艺进行了优化,结果表明α-淀粉酶量、糖化酶量和液化温度对木薯淀粉水解有显著影响。当淀粉酶量为756 U/g,糖化酶量为602 U/g,液化温度为92°C,其水解DE值达到97.3%。以该水解液进行皮状丝胞酵母B3(T.cutaneum B3)油脂发酵时,其生物量和油脂产量分别为16.38 g/L和7.22 g/L,比葡萄糖作为碳源的生物量和油脂产量高46.25%和41.12%,利用木薯淀粉水解液作为新型发酵碳源生产微生物油脂是一种理想的途径。     

Comparison of an alkaline picrate and a pyridine-pyrazolone method for the determination of hydrogen cyanide in cassava and in its products

A determination of hydrogen cyanide in fresh cassava tissues and in processed cassava products using an alkaline picrate procedure and a pyridine-pyrazolone method which uses Conway vessels has been made. Results obtained for the fresh cassava tissues by the two methods were similar. Statistically significant higher values for processed cassava products were obtained by the alkaline picrate method which measured both glycosidic and non-glycosidic cyanide. The suggestion is reaffirmed that hydrogen cyanide in processed cassava products may exist in two forms: glycosidic and non-glycosidic (entrapped) cyanide.     

Isolation and Physico-chemical Characterization of Coleus Tuber Starch

The physico-chemical properties of starch isolated from Coleus tuber (Coleus parviflorus) has been investigated. The yield of extracted starch is 14.4% from the raw tuber. The starch behaves like a cereal starch. The granules are 2.5–17.5 um in diameter and show “A” pattern on X-ray diffraction. The starch exhibits limited two stage swelling and rapid dissolution in DMSO. It has an iodine affinity of 3.63, and the amylose content is 18.18%. The paste viscosity was stable during cooking and has a positive set back unlike cassava starch. The starch was somewhat resistant to amylase attack.     

An automated enzymic assay for determining the cyanide content of cassava (Manihot esculenta crantz) and cassava products

An automated enzymic method for the analysis of cyanide in cassava and cassava products is described. A total of 300 analyses a day can be handled easily. A wide range of free (nonglycosidic) or bound (cyano-substituted glycosides) cyanides (0.4–40 μg HCN ml^?1) can be assayed in the extracted solutions. The upper limit of detection for the bound cyanide can easily be increased by another three-fold by assaying it under partial hydrolysis conditions. The two enzymic methods, manual and automated on Technicon's AutoAnalyzer, agreed well for the free and the bound cyanide in the leaf and the peeled storage root samples.     

Cyanide detoxification in cassava for food and feed uses

Cassava (Manihot esculenta Crantz) is an important tropical root crop providing energy to about 500 million people. The presence of the two cyanogenic glycosides, linamarin and lotaustralin, in cassava is a major factor limiting its use as food or feed. Traditional processing techniques practiced in cassava production are known to reduce cyanide in tubers and leaves. Drying is the most ubiquitous processing operation in many tropical countries. Sun drying eliminates more cyanide than oven drying because of the prolonged contact time between linamarase and the glucosides in sun drying. Soaking followed by boiling is better than soaking or boiling alone in removing cyanide. Traditional African food products such as gari and fufu are made by a series of operations such as grating, dewatering, fermenting, and roasting. During the various stages of gari manufacture, 80 to 95% cyanide loss occurs. The best processing method for the use of cassava leaves as human food is pounding the leaves and cooking the mash in water. Fermentation, boiling, and ensiling are efficient techniques for removing cyanide from cassava peels.     

An enzymatic assay for the total cyanide content of cassava (Manihot esculenta Crantz).

An enzymatic assay for the cyanide contents of cassava parenchymal tissue (peeled root), cassava peel or cassava leaves is described. The material is homogenised in orthophosphoric acid; filtered through glass-fibre paper and aliquots of the filtrate are neutralised and incubated with exogenous linamarase for 15 min. The cyanogenic glucosides present are hydrolysed to free cyanide which is estimated spectrophotometrically. The acid extraction solution inactivates endogenous linamarase, and assay of aliquots without enzyme treatment gives the free (non-glycosidic) cyanide contents of the extracts. The acid extracts are stable for at least 4 days at 4°C, and the steam-distillation/aspiration of earlier methods is unnecessary. The detection limit is < 0.01 mg (0.1 parts 10^?6) cyanide per 100 g fresh weight and peeled root, and 40-50 samples per day can be handled easily. Analyses of eight cultivars indicated longitudinal and radial cyanide gradients in the roots, and the problem of sampling bulky roots is discussed.     

Xanthan Production by Mutant Strain of Xanthomonas campestris TISTR 840 in Raw Cassava Starch Medium

Raw cassava starch was used as carbon source in growing Xanthomonas campestris TISTR 840 for xanthan production due to its cheap price and mass production in Thailand. However, xanthan production with raw cassava starch yielded low content (4.31 g/l). A low level of amylase was detected in the XOL medium of X. campestris when raw cassava starch was used. Treatment of X. campestris TISTR 840 with ethyl methansulfonate resulted in the isolation of Xc-M, a strain that showed highest amylase overproduction. When cultured in bioreactor with a medium containing raw cassava starch, the growth of Xc-M cells was significantly higher than that of the wild type. The mutant produced 3.46- and 1.39-fold increased amylase activity and xanthan yield, respectively. Xc-M is useful for xanthan production in media containing raw starch as a carbon source.     

黑曲霉固态发酵橘皮生产纤维素酶及淀粉酶

以橘皮为原料,以黑曲霉AS3.3928为生产菌株,采用固态发酵法生产纤维素酶和淀粉酶。通过单因素试验考察固态发酵培养基中橘皮含量、培养基含水量、接种量及发酵时间4个因素对纤维素酶和淀粉酶活力的影响。在单因素试验基础上,通过正交试验最终确定最优产酶条件为：固态发酵培养基中添加16g橘皮,并加入5mL无菌水使培养基初始含水量为64mL/100g,黑曲霉接种量15%,发酵60h。在此发酵条件下所产纤维素酶活力可达1816U/g,淀粉酶活力达196U/g。结果表明,利用黑曲霉固态发酵橘皮,非常有利于纤维素酶和淀粉酶的生产。