Assessment of Bacterial and Fungal Spoilage of Some Nigerian Fermented and Unfermented Foods

Vol. 8(3), pp. 140-147, March 2014 DOI: 10.5897/AJFS2013.1059 ISSN 1996-0794 Copyright © 2014 African Journal of Food Science Author(s) retain the copyright of this article http://www.academicjournals.org/AJFS Full Length Research Paper Assessment of bacterial and fungal spoilage of some Nigerian fermented and unfermented foods Adebayo CO1, Aderiye BI2 and Akpor OB3* 1Department of Science Technology, Federal Polytechnic, Ado-Ekiti, Ekiti State, Nigeria. 2Department of Microbiology, Ekiti State University, Ado-Ekiti, Ekiti State, Nigeria. 3Department of Biological Sciences, Landmark University, Omu-Aran, Kwara State, Nigeria. Received 19 July, 2013; Accepted 26 February, 2014 The study was aimed at evaluating the microbial spoilage of selected Nigerian fermented and unfermented foods. A total of four fermented and unfermented food samples were used for this investigation. Microbial and sensory evaluations of the food products during storage were carried out using standard procedures. During storage, the bacteria counts were observed to range from 2.2 × 105 to 4.8 × 105 CFU/mL and from 2.5 × 103 to 5.0 × 104 CFU/mL, for the unfermented and fermented food products, respectively. Similarly, the fungal counts ranged from 1.8 × 103 to 2.9 × 103 CFU/mL and from 0 to 5.70 × 103 CFU/mL for the unfermented and fermented food samples, respectively. Klebsiella aerogenes, Lactobacillus plantarum, Leuconostoc sp., Micrococcus varians, Proteus mirabilis, Streptococcus faecalis, Staphylococcus epidermidis, Aspergillus niger, Aspergillus flavus, Cladosporium herbarum, Geotrichum candidum, Mucor mucedo, Neurospora sitophilia and Penicillium sp. bacteria and fungi that were recovered from the food samples during storage. The sensory evaluation of the food products showed the fermented ones being more acceptable to panelists than the unfermented ones. This could indicate that the palatability of the fermented food samples only experienced slight or no changes during storage, when compared to the unfermented ones. Key words: Fermented food, unfermented food, microbial spoilage. INTRODUCTION It is reported that fermented foods constitute about 25% produced at household levels, the issue of hygiene is a of the foods consumed worldwide. Fermented foods have major concern (All and Dardir, 2009; Gadaga et al., many advantageous attributes, which include improved 2004). nutritional value and safety against pathogens over non- Both fermented and unfermented food products are fermented foods. Generally, these foods are normally known to be susceptible to spoilage during storage. Their considered to be safe against foodborne diseases spoilage during storage is attributed to the presence of because of the advantage of low pH, which is due to the microorganisms and extracellular enzymes produced, presence of organic acids produced during fermentation. which breakdown the food product into new substances In Africa, because a majority of the fermented foods are resulting into changes in their organoleptic properties *Corresponding author. Email: [email protected]. Tel: +2348099189171. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Adebayo et al. 141 (Fadahunsi et al., 2013). Chance inoculation, activities of food products were purchased from the local market in Ado-Ekiti, spoilage organisms and the humid condition in the Ekiti State in Nigeria. To ensure uniformity and prevent any pre- Tropics are some of the factors responsible for spoilage storage contamination, the purchased raw food products were prepared locally in the laboratory using aseptic techniques. Each of of these foods during storage. While starter cultures have the prepared food samples was transferred into and wrapped with been used to ensure uniformity in the composition of sterile polythene bags (ca 0.2 mm thick), while some were left some fermented foods, their reduced shelf life still unwrapped. Food samples from ‘Eko’ and ‘Kati’ were wrapped in remains a major problem worldwide. The ingestion of the leaves of Thaumatoccus daniella. This was to ensure that the products contaminated with these microorganisms could samples were in the same state as they were normally packaged in the locality. Detail description of the food products and their be a potential health threat hence there is the need to preparation have been described elsewhere (Aderiye and Lalaye, control microbial contamination of fermented foods and 2003). All the food products were stored under hygienic conditions feeds. at refrigeration and ambient temperatures. Filamentous moulds and yeast are common spoilage Microbiological analyses were carried out using conventional organisms of food products as fermented milk products, microbiological procedures. The total microbial count on the food cheese, bread, stored crops and feed such as hay and sample was determined by the pour plate method using standard microbiological techniques. Nutrient agar and Malt extract agar silage (Filtenborg et al., 1996). Penicillia and Aspergilli were used to culture bacteria and fungi, respectively. All bacterial species have been reported as spoilage organisms and fungal counts were expressed as colony forming units per during storage of a wide range of foods where they may milliliter (CFU/mL) and propagules and cells/mL respectively. In all produce a number of mycotoxins (Samson et al., 2002). cases, each analysis was carried out in triplicates. The isolation Several authors (Pitt and Hocking, 1999; Magnusson and and identification of the bacteria and fungi were carried out as Schnurer, 2001) have also implicated yeasts such as described elsewhere (Barnett and Hunter, 1992; Burgess and Sum, 1994; Holt et al., 1994). The occurrence of each isolate in the food Candida parapsilosis, Rhodotorula mucilaginosa, samples was determined as a percentage of the total number of Kluyveromyces marxians and Derbaromyces hansenii as food samples and recorded as the frequency of occurrence. The common spoilage organisms of yoghurt and other frequency of occurrence of isolates in the food samples was fermented food products. calculated using the following formula: Apart from food spoilage, health hazards from fungal mycotoxins had been well documented. For instance, the large consumption of grains infected with sclerotia of Claviceps pupurea caused several thousand deaths in Sensory properties such as appearance, colour, odour, taste, the 10th and 11th century in central Europe (Pohland, texture and general acceptability were also used in an 11-point ‘Hedonic’ scale to test the acceptability and rejection of the food 1993). It is estimated that between 5 and 10% of the samples. The detection of spoilage was done through physical world’s food products is lost due to fungal deterioration examination of the stored food samples. The wrapped food sam- (Pitt and Hocking, 1999). The growth of these undesi- ples were observed daily for changes in appearance, texture, rable fungal species in foods has been a worldwide aroma and taste. The day of onset of each defect or sign of spoi- concern over the years because of its effects on man’s lage and the types were recorded. health and consequent economic loss due to food sto- Each of the experiments was carried out in triplicates and conducted twice. All the statistical analyses were carried out using rage. During food spoilage, which is a metabolic process, the SPSS computer statistical software. The comparison of means the spoilt food becomes undesirable and unacceptable was done using the One-Way Analysis of Variance Test. for human consumption due to changes in sensory characteristics. Fermented foods such as gari, ogi, fufu and mawe are RESULTS found all over the world. Fermentation has offered a means of food security in Nigeria; where over 52% of The microbial quality of the food samples is shown in respondents in a previous study in 2003 indicated that Figures 1 and 2. When the food samples were examined about 25% of their monthly income is spent on fermented within one hour of processing, no microbial contamination food products (Aderiye and Laleye, 2003). This paper was recorded. As shown in Figure 1, in all the food sam- therefore examines and discusses the desirability of ples, bacterial colonization was observed within 24 h after consuming part of spoiled fermented food products as production. The bacterial counts in the food samples reported by Aderiye and Laleye (2003). It is also aimed at were observed to increase with increase in storage time. evaluating the types and extent of microbial spoilage of At the end of 96 h storage period, the bacterial counts some selected Nigerian fermented and unfermented from the unfermented food samples ranged from 2.2 × foods. 105 to 4.8 × 105 CFU/mL, for yam and pounded yam, respectively. In the fermented food samples, the bacterial count was observed to range from 2.5 × 103 to 5.0 × 104 MATERIALS AND METHODS CFU/mL, for ‘Kati’ and ‘Eba’, respectively (Figure 1). In all A total of eight different food samples, divided into unfermented cases, the bacterial counts in the unfermented food sam- (pounded yam, yam, rice and beans) and fermented (‘Eba’, ‘Eko’, ples were significantly higher than those in the fermented ‘Fufu’ and ‘Kati’) food products were used in this study. The raw food samples (P≤0.05). Even after 96 h storage, ‘Eba’ still 142 Afr. J. Food Sci. Figure 1. Average bacterial counts of the food samples during the period of storage. Figure 2. Average

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