comparative effects of oven drying and sun drying on ...

ISSN: 1579-4377

COMPARATIVE EFFECTS OF OVEN DRYING AND SUN DRYING ON THE MICROBIOLOGICAL, PROXIMATE NUTRIENT AND MINERAL COMPOSITION OF TRYPANOTONOUS SPP. (PERIWINKLE) AND CRASSOSTREA SPP. (OYSTER). 1

B. C. Adebayo-Tayo and A.A. Ogunjobi Department of Microbiology, University of Uyo. Uyo Akwa Ibom State, Nigeria, 2 Department of Botany & Microbiology, University of Ibadan, Ibadan, Nigeria Author for correspondence: E-mail: [email protected]

ABSTRACT Comparative effect of oven drying and sun drying on microbiological, proximate nutrient and mineral composition of Trypanotonous spp and Crassostrea spp was conducted. The shellfishes were sun dried and oven dried and preserved for 28 days. Total bacterial count of freshly harvested periwinkle and oysters were 1.20 x 105 and 2.20 x 105cfu/g respectively. The level of coliform was generally high ranging from 3.0 x 104 of the total load in Trypanotonous spp to 5.3 x104 in Crassostrea spp while the salmonellae count ranged from 2.0 x 104 in Trypanotonous spp to 4.5 x 104 in Crassostrea spp. The total bacterial count for oven dried periwinkle (ODP) and oven dried oyster (ODO) during the preservation period varied from 1.0 x 101 – 4.3 x 102 and 3.0 x 101 – 9.0 x 103cfu/g respectively and for sun dried periwinkle (SDP) and sun dried oyster (SDO), it ranged from 1.6 x 101 – 4.8 x 103 and 2.2 x 101 – 2.0 x 104cfu/g respectively. The fungal count for oven dried and sun dried periwinkle ranged from 3.5 – 6.5 x 101 and 2.2 – 6.4 x 102 cfu/g respectively and for oven dried and sun dried oyster (ODO and SDO) ranged from 2.5 x101 - 2.8 x 102 and 1.1– 3.6 x 102 cfu/g respectively. The organism isolated from freshly harvested samples was E. coli, Pseudomonas aeruginosa and Salmonella paratyphi and Bacillus cereus. The microbial isolate at the end of preservation was B. cereus and M. virians while the fungi isolates were A. niger, A. vesicolor and P. vindicatum in both oven dried and sun dried samples. The results of microbial analysis revealed fresh periwinkle and oysters to have higher microbial growth than preserved samples. Preservation was very effective in eliminating bacteria from the shellfishes, no growth was observed within the first 24h of preservation. Protein content of ovendried and sun dried periwinkle ranged from 57.96 – 60.04 and 61.28 – 72.66µg/l for oven dried and sun dried oyster. The Ca, K, P, and Fe content ranged from 202.18 – 680.85, 410 – 475.7, 48.82 – 81.01 and 152.0 – 650.0µg/l respectively. Proximate analysis revealed that oven dried shellfishes are nutritionally richer than fresh and sun dried samples and oysters are nutritionally richer than periwinkle. KEYWORDS Oyster, Periwinkle, Ovendried, Sundried, Proximate, Mineral.

Adebayo-Tayo et al. EJEAFChe, 7 (4), 2008. [2856-2862]

INTRODUCTION Periwinkles (Tympanotonus spp.) and oyster (Crassostrea spp.) represent one of the most important shellfish’s resources of the world. In West Africa, periwinkles and oysters are the most dominant of the aquatic mollusks, occurring widely in both fresh and brackish water (Buchaan 1954, Okon 1987). The term shellfishes comprise crustaceans (shrimps, crabs, lobsters, crawfish etc) and mollusks (bivalves, squids, snails etc) (Liston 1956) and possess single (univalve) or double (bivalve) shells for a covering. The oysters dominate the temperate and warm coastal waters of all oceans while periwinkles are marine mollusks dominate in brackish waters. They are represented in lagoons, estuaries and mangrove swamps by two genera, Tympanotonous and Pachymelinia (Buchanan, 1954). Oysters are represented by two genera, Crassostrea and Ostrea (Daud, 1989). Since these fishes or shellfishes are got from the sea and eaten as food, they are termed seafood. Seafood forms a major source of protein to both Riverine dwellers and the public at large. They lying the brackish and freshwater. The practice of preserving food can be traced from prehistoric times, when fruits and vegetable were dried, cereal grains were parched and fish and game were salted and dried. The post harvest technologies in fish preservation have been remarkable and led to reduce wastage and improve eating quality of fish (Jones and Disney, 1997). Available preservation technologies had helped to ensure that not only plentiful and large variety of fish is available throughout the year, but desirable quality of fish in term of flavor, odor, taste, texture and appearance can be obtained, (Bostock et al., 1987). Therefore, considering the massive consumption / demand of edible shellfishes, its commercial and industrial importance, this present work was undertaken to comparatively evaluate the effects of two preservation techniques – sundrying and ovendrying on microbiological quality as well as the proximate nutrient and mineral composition on fresh and preserved Trypanotonous spp and Crassostrea spp. MATERIALS AND METHODS Sample Collection One thousand pieces each of Trypanotonous spp (periwinkle) and Crassostrea spp. (Oyster) samples used in this study were collected from Itu River, in Itu, a famous shellfish producing area in Akwa Ibom state, Nigeria. The samples were collected in sterile bucket and taken to the laboratory for analysis within 3 hour of procurement. Processing of samples Three sets of scrubbed periwinkle and oyster made up of two hundred pieces each were separated. One set of fresh periwinkle and oyster were scrubbed, rinsed and the meat was aseptically extracted using a sterile knife as described by APHA (1970). The samples were used for further analysis.

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Another set of two hundred pieces each of periwinkle and oyster sample were sun dried (SDP and SDO) as described by Kordylas (1990). The freshly extracted meat were placed in a tray fitted into a drying rack and a clean net was placed over the drying rack to keep flies and other contaminants from getting in contact with the shellfishes. The samples were then exposed to the sun on a raised platform till the samples were completely dried. Another set of two hundred pieces each of freshly extracted periwinkles and oyster (meat) was subjected to oven drying (ODP and ODO). The meat was placed in dishes and was dried in the oven at 1270C as described by Kordylas (1990). Packaging: Clean polythene bags, which produced air/moisture better packaging, were bought locally. 50 pieces each of the sun dried and oven dried shellfishes samples from each treatment group (SDP1, SDO2, ODP3 and ODO4) were divided into 5 group for each of the storage intervals (7, 14, 21 and 28 days) and were packed aseptically in a sterile polythene bag separately and then sealed with a sealer and labeled and stored in an environmental cabinet set at 30 (+ 20C) and 75% to 85% relative humidity throughout the storage period. Microbiological analysis Microbiological analyses of fresh, ovendried and sundried samples were carried out in triplicate on 50g samples (fresh, ovendried and sundried respectively) which were blended with 450ml of sterile 0.1% peptone water as describe in the Bacteriological Analytical Manual (FDA, 1984). Pour plates were prepared from 10- fold dilutions in nutrient agar (oxoid) for total bacteria count, MacConkey agar (oxoid) for total coliform counts and Salmonella /Shigella agar (oxoid) for Salmonella/Shigella counts were made after incubation at 370C for 24h. Colonies were selected randomly. Bacteria cultures were characterized and identified using various morphological and biochemical tests such as gram stain, spore stain, motility, catalase, coagulase, indole, MR-VP, urease, citrate, oxidase and sugar fermentation tests The isolates were identified with reference to Cowan and Steel’s Manual for the identification of Medical Bacteria (1985) and Fawole and Oso’s laboratory manual (1988). Proximate composition was carried out according to the method of A.O.A.C (1975). This includes determination of pH, moisture content, ash content, crude protein, and fiber, fat, total carbohydrate contents. Mineral content such as potassium, calcium, phosphorus and iron. RESULTS The result of microbiological study of fresh periwinkle and oyster samples were shown in Table 1. Table 1. Total count of microbial groups in the fresh shellfish’s samples Key: FP=Fresh Periwinkle, FO=Fresh Oyster. Samples Total bacteria count Coli form count cfu/g Salmonellae count cfu/g FP 1.20 x 105 3.0 x 104 1 x 104 5 4 1.35 x 10 2.0 x 10 2.0 x 104 5 4 FO 2.20 x 10 4.0 x 10 3.0 x 105 5 4 1.72 x 10 5.3 x 10 4.5 x 105

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Total bacterial populations of the samples varied from 1.30 x 105 – 1.20 x 108 for fresh periwinkle and 1.72 x 108 – 2.21 x 108 for fresh oyster respectively. Fresh oyster had the highest level of total viable count, coliform and Salmonella shigella density. Table 2 shows the total count of microbial groups in the preserved shellfish samples. Table 2: Total count of microbial species in the preserved shellfish samples 7 days

14 days

21 days

Samp les

Total Viable Count

Colifor m Count

Salmon ella Count

Fun gal Cou nt

Total Viable Count

Coli form Cou nt

Fun gal Cou nt

Total Viable Count

Coli form Cou nt

-

-

-

1.1 x 102 1.5 x 102 6.0 x 102 6.8 x 102 2.9 x 102 3.0 x 102 1.8 x 103 1.5 x 103

-

-

-

2.2 x 102 1.2 x 102 3.0 x 102 3.2 x 102 6.0 x 102 6.2 x 102 3.5 x 103 3.0 x 103

Salm onell a Cou nt

ODP

1.0 x 101 2.5 x 101 1.6 x 101 1.9 x 101 3.3 x 101 3.0 x 101 2.2 x 101 2.5 x 101

Sal mon ella Cou nt

-

-

SDP ODO SDO

28 days Fungal Count

Total Viable Count

Coli form Cou nt

F

7.0 x 101 6.5 x 101 2.2 x 102 2.3 x 102 2.8 x 101 2.5 x 101 1.1 x 102 1.5 x 102

4.0 x 102 4.3 x 102 4.1 x 103 4.8 x 103 9.0 x 103 9.0 x 103 2.1 x 104 2.0 x 104

Salm onell a Cou nt

-

-

5 3 6 3 4 2 3 3

Key: ODP = Ovendried periwinkle, SDP = Sun dried Periwinkle, ODO = Oven dried Oyster, SDO = Sun dried Oyster , - = No Growth

Total bacterial population of the oven dried periwinkle varied from 1.0 x 101 – 4.3 x 10 and 3.0 x 101 – 9.0 x 103cfu/g for sun dried periwinkle, 1.6 x 101 – 4.8 x 103 and 2.2 x 101 – 2.0 x 104cfu/g for oven dried and sun dried oyster respectively. The fungal count for oven dried and sun dried periwinkle ranged from 3.5 – 6.5 x 101 and 2.2 – 6.4 x 102 cfu/g respectively while for oven dried and sun dried oyster (ODO and SDO) it ranged from 2.5 x101 - 2.8 x 102 and 1.1– 3.6 x 102 cfu/g respectively. The bacteria isolates identified in the fresh periwinkle and oyster samples include E. coli, Pseudomonas aeruginosa and Salmonella paratyphi, while the bacteria isolates identified in the preserved periwinkle and oyster samples include Bacillus cereus, Micrococcus virians, Aerococus virians and Micrococcus luteus. Bacillus cereus was predominant in the samples after preservation. The fungal isolates were, Saccharomyces sp, Aspergillus niger, Aspergillus vesicolor and Penicillium vindicatum Penicillium sp, and Aspergillus flavus. Penicillium sp was predominant after preservation (Table 3). Preservation was very effective in eliminating bacteria from the shellfishes, no growth was observed within the first 24hrs of preservation. Proximate nutrient/mineral composition of fresh and preserved shellfish sample were shown in Table 4. 2

Table 3. Microbial isolates from fresh and preserved periwinkle and oyster samples Samples Microbial isolates FP Pseudomonas aeruginosa FO E. coli, Salmonella paratyphi, Bacillus cereus, Pseudomonas aeruginosa ODP Bacillus cereus, SDP Bacillus cereus, Micrococcus virians, Aerococus virians, Aspergillus vesicolor ODO Bacillus cereus, Penicillium vindicatum SDO Bacillus cereus, Micrococcus virians, Aerococus virians, Aspergillus niger Key: FP= Fresh periwinkle, FO = Fresh oyster, ODP = Ovendried periwinkkle, SDP = Sun dried Periwinkle, ODO = Oven dried Oyster and SDO = Sun dried Oyster .

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Table 4: Physicochemical/nutritional composition of fresh and preserved shellfish sample

Mineral Composition (µg/g) Moisture Ash Crude Crude Ca P K Fe content content fiber protein (%) (%) (%) (%) 8.68 74.0 3.40 0.39 41.396 202.18 229 610.60 650.00 7.23 20.2 10.60 0.38 57.962 320.20 68.72 410.20 450.00 7.05 22.5 10.50 0.37 60.04 430.16 48.82 508.40 485.50 8.95 78.0 4.53 0.28 63.036 680.85 81.01 3000.00 152.0 7.20 22.8 9.00 6.36 61.282 672.340 80.07 3214.29 302.50 6.83 25.3 10.10 6.30 72.667 489.362 58.29 4757.13 572.50 Key: FP= Fresh periwinkle, SDP = Sun dried Periwinkle, ODP = Ovendried periwinkle, FO =fresh oyster, ODO = Oven dried Oyster and S

Sample FP SDP ODP FO SDO ODO

pH

Sun dried Oyster .

DISCUSSION The periwinkles and oysters used in this study are important commercial mollusks that are widely eaten by mankind from time immemorable especially by people of the Riverine areas of the world, as good sources of protein. Variation in the microbial load between the shellfishes can be attributed to the variation in micro environmental condition encountered by these organisms, and the self-purification of the water body. Results obtained from this work revealed that though these mollusk shellfishes are good and cheap sources of protein, they could also harbor a lot of food poisoning organisms that pose serious health hazards to man, since they contain permissible nutrients that support microbial growth. The higher level of bacteria in fresh oyster could be due to the fact that deposits feeders are known to ingest sediments and use organic matters and microorganisms in the sediment as food (Jeffrey, 1995). Also oyster lives in freshwater which support the proliferation of a broader spectrum of microorganisms as opposed to brackish water in which periwinkle species lives (Nester et al., 1983). The oyster dominates the temperate and warm coastal waters of all oceans while periwinkles as marine mollusks dominate in brackish waters. They are represented in lagoons, estuaries, and mangrove swamps by two genera, Tympanotonus and Pachymelinia (Buchanan, 1954). Oysters are represented by two genera, Crassostrea and Ostrea (David, 1989). Adebayo – Tayo et al., (2006) has reported higher level of contamination in periwinkle from different creeks. Furthermore, there are greater pollution-causing activities like bathing, washing and sewage discharge in the fresh water environment where oyster is harvested than in brackish water environment. Jay (1978) and Ekanem and Adegoke (1995) have reported that the level of contamination of shellfish depends on the extent of pollution in the growing waters since these water may contain untreated and industrial wastes and as filter feeders, there is a great tendency that these shellfishes will accumulate a number of food poising and pathogenic organisms from waters impacted by sewage pollution and biotoxins produced by some species of phytoplankton, that they feed on which accumulate in their tissues when ingested as food. These shellfishes are apparently unaffected by the toxin but on consumption of these toxins cause a disease known as paralytic shellfish poisoning in human.

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The organisms isolated from the fresh samples include Eschericial coli,Pseudomonas aeruginosa Salmonella paratyphi Bacillus cereus, and Micrococcus virians,. Most of the microbial isolates in this study has been isolated from periwinkle in the previous study except Enterobacter aerogenes (Adebayo – Tayo et al., 2006). These organisms are common in seafood, though Bacillus cereus can cause intoxication. The occurrence of enteric organisms in the shellfish’s samples was an indication of the pollution of their overlying water with untreated faecal waste and sewage. All the organisms isolated have health implication for man except Micrococcus virians, which have not been associated with human infections. These organisms are likely to have been introduced into the environment by bathers and surfers who use these creeks for reactional purposes. For the preserved samples, the method used was effective in reducing the microbial load of the shellfishes. The organisms isolated from the preserved samples include Bacillus cereus, Micrococcus virians, Aerococcus viridans, Aspergillus niger, Aspergillus vesicolor and Penicillium vindicatum. Most of these organisms especially Aspergillus sp produces toxins (mycotoxins) and could cause mycotoxicoses in human on accumulation in the body. Fungal growth was observed in the samples from 21st day of storage. There was a reduction in moisture content during oven drying and sun drying, thereby causing a reduction in water activity; hence there was no available moisture for microbial growth/metabolism (Jay, 1978). Occurrence of Aspergillus niger and A. vesicolor in sun-dried samples can be attributed to contamination during sun drying It was reported that Aspergillus niger is responsible for aspergillosis (Alice, 1977), usually an infection of the external ear (otomycosis) which may result in ulceration of the lining of the ear canal and perforation of the lymphatic membrane. The reduction in fungal count of oven dried oyster after 21st day could be attributed to the presence of Penicillium spp, which produced inhibitory substances, which could hinder the growth of other organisms. The microbial load of the fresh samples, from the results obtained, when compared with the food and Drug Administration (FDA, 1989b) standard of standard plate count of