Ogbo Frank C
Department of Food Science and Technology, Ebonyi State University, P.M.B., 053, Abakaliki, Nigeria.
Int J Food Microbiol. 2003 Dec 15;89(1):85-90. doi: 10.1016/s0168-1605(03)00113-2.
Alkali pretreatment of cassava roots before retting and addition of sodium nitrate during retting were used to manipulate the metabolism of microorganisms involved in cassava (Manihot esculenta Crantz) retting, as a method for removing the characteristic offensive odour of retted cassava products. Odour was assessed by organoleptic methods. The characteristics of fermentation of cassava by the traditional method (control) were as follows; aerobic mesophilic count (APC) on nutrient agar (NA) at 30 degrees C/48 h, attained a maximum of 2.3 x 10(7)/ml retting juice while counts on de Man Rogosa and Sharpe agar (MRS) at 30 degrees C/48 h were 1.6 x 10(8)/ml. Maximum titrable acidity was 0.062% lactic acid by weight of retting juice. Cassava was retted in 3 days and the product exhibited characteristic offensive odour. Addition of NaNO3 into retting water effectively removed odour at a concentration of 0.3 g/l. Maximum APC on NA/30 degrees C/48 h was 6.8 x 10(6)/ml. Counts on MRS/30 degrees C/48 h exceeded 2.4 x 10(9)/ml. Retting was complete in 3 days with a final titrable acidity of 0.068% of retting juice. Removal of odour likely resulted from selection of homo-fermentative lactic acid bacteria, thus producing mostly odourless lactic acid. Alkali pretreatment of roots before retting was efficacious in removing odour at a concentration of 10 g/l for 30 min. This fermentation was characterized by APC on NA/30 degrees C/48 h of 5.4 x 10(6)/ml; MRS/30 degrees C/48 h reached a maximum of only 10 x 10(4)/ml and correspondingly low titrable acidity of 0.003%. Low counts of lactic acid bacteria correlate well with the absence of odour in this sample. Both treatments did not adversely affect the detoxification process, yielding "foo-foo" with HCN levels lower than 10 mg/kg. Residual nitrates and nitrites of 30 mg/kg in the sodium nitrate-treated sample were also within the safe limits of 156 mg/kg allowed in many countries. Organoleptically improved samples were acceptable to the public.
木薯根在沤制前进行碱预处理，并在沤制过程中添加硝酸钠，以调控参与木薯（Manihot esculenta Crantz）沤制的微生物的代谢，作为一种去除沤制木薯产品特有的刺鼻气味的方法。通过感官方法评估气味。传统方法（对照）沤制木薯的发酵特征如下：在30℃/48小时的营养琼脂（NA）上的需氧嗜温菌数（APC），在沤制汁中最高达到2.3×10⁷/ml，而在30℃/48小时的德氏乳杆菌、罗格斯氏菌和夏普氏琼脂（MRS）上的菌数为1.6×10⁸/ml。最大可滴定酸度为按沤制汁重量计0.062%的乳酸。木薯在3天内沤制完成，产品呈现出特有的刺鼻气味。在沤制水中添加0.3 g/l浓度的硝酸钠可有效去除气味。在NA/30℃/48小时上的最大APC为6.8×10⁶/ml。在MRS/30℃/48小时上的菌数超过2.4×10⁹/ml。沤制在3天内完成，最终可滴定酸度为沤制汁的0.068%。气味的去除可能是由于选择了同型发酵乳酸菌，从而主要产生无味的乳酸。木薯根在沤制前进行碱预处理，以10 g/l的浓度处理30分钟可有效去除气味。这种发酵的特征是在NA/30℃/48小时上的APC为5.4×10⁶/ml；在MRS/30℃/48小时上最高仅达到10×10⁴/ml，相应地可滴定酸度较低，为0.003%。乳酸菌数量低与该样品中无气味密切相关。两种处理均未对解毒过程产生不利影响，所生产的“富富”（一种木薯食品）中的氰化氢水平低于10 mg/kg。硝酸钠处理样品中30 mg/kg的残留硝酸盐和亚硝酸盐也在许多国家允许的156 mg/kg的安全限量范围内。感官上得到改善的样品为公众所接受。
