Optimal storage conditions for cocoa cake with shell, palm kernel cake and copra cake as poultry and livestock feed in Ghana

P A Wallace, E K Adu* and S W A Rhule

CSIR-Animal Research Institute, P. O. Box AH 20, Achimota, Accra, Ghana
* Correspondence: Council for Scientific and Industrial Research (CSIR), Animal Research Institute, P. O. Box AH 20, Achimota, Ghana
nhyirapapa@yahoo.com

Abstract

The optimum storage conditions for three oil seed cakes namely copra cake (CC), palm kernel cake (PKC) and cocoa-cake-with-shell (CCWS) were studied under four different conditions: (Deep freezer, DF, -15±1^oC), (Refrigeration, REF, 5±1^oC), (Air condition, AC, 19±1^oC) and (Room temperature, RT, 25±1^oC). Samples were chemically analysed fortnightly over a 6 month period for proximate, gross energy, Ca, P and free fatty acid composition.

Among the parameters analyzed under proximate analysis, moisture, ether extract and crude protein contents which have potential to undergo major alterations with time were not significantly (P > 0.05) influenced by all the storage conditions studied irrespective of the oil seed cake considered. On the other hand, the free fatty acid content was significantly (P<0.03) affected by storage conditions with the values increasing with time. The most significant change occurred when storage was done at RT.

The study indicated that CCWS should not be stored longer than 2 weeks when kept under RT conditions whereas CC may be stored up to 6 and 8 weeks under REF and DF respectively. PKC could be well preserved under DF for as long as 10 weeks while under RT, storage should be less than two weeks.

Key words: crude protein, ether extract, free fatty acid, moisture content, oil seed cake, storage condition

Introduction

Agro-industrial by-products (AIBPs) have been reported to be worthy substitutes for grains and fish meal for domestic animal nutrition and are considered to have considerable potential (Hutagalung et al 1984). One such group of AIBPs that is receiving much attention in the poultry and livestock industry is the oil seed cakes such as palm kernel cake (PKC), copra cake (CC) and soybean cake. Cocoa by-products such as cocoa pod husks and cocoa-cake-with-shell (CCWS) are another group of AIBPs with potential for animal feeding (Wong and Zahari 1997, Rhule et al 2005). As a result of the relatively high residual oil, such seed cakes have been reported to be a satisfactory and economic substitute for high energy feedstuffs such as maize. They are reportedly cheap, readily available and a valuable source of fat-soluble vitamins (Okai and Vroom 1979).

One major setback affecting the poultry and livestock enterprise is the preservation and storage of feed ingredients. Improper storage of these could result in the incidence of moulds, and rancidity with its attendant unpleasant taste and odour (Pearson 1985). Feeding rancidified diets reportedly affect dietary essentials, cause dermatitis, alter intestinal flora as well as interfere with nutritional properties of fats (Greenberg and Frazer 1953). Moreover, food products naturally undergo various chemical and enzymatic reactions which to a large extent determine their acceptability, shelf life and safety due to factors such as the oxidation of double/triple bonds of unsaturated lipids, high moisture content and other factors (Tomassi 1988, Kolapo and Sanni 2007). With increased awareness of the use of oil seed cakes in livestock and poultry feeding, the need to have vital but beneficial baseline information on the optimal storage conditions and keeping quality is therefore imperative. There is, however, lack of information on the optimal period and best conditions under which palm kernel cake (PKC), copra cake (CC) and cocoa-cake-with shell (CCWS) could be stored even though their inclusion in feed formulations is receiving increasing attention among farmers in most tropical countries where they are found. The aim of this study, therefore, was to determine the optimum conditions under which PKC, CC and CCWS could be stored using the potential changes in proximate, gross energy, calcium (Ca) and phosphorus (P) and free fatty acid levels as the indices of evaluation.

Materials and methods 

Sample collection and treatment

Freshly produced cocoa-cake-with-shell (CCWS) was obtained from WAMCO (West Africa Mills Company Ltd, Takoradi, Ghana) while palm kernel cake (PCK) and copra cake (CC) were obtained from Tringo, an agro-based company sited in Accra, Ghana. The samples were ground to pass through a 30 mm mesh sieve on a laboratory hammer mill. Each sample was then divided into four parts and kept under four different storage conditions namely deep freeze (DF) at –15±1^oC, refrigeration (REF) at 5±1^oC, air condition (AC) at 19±1^oC and room temperature (RT) at 25±1^oC.

Chemical Analysis

Free fatty acid (FFA), proximate composition, gross energy, calcium and phosphorus were determined on freshly obtained cakes immediately after production. Thereafter, the same parameters were monitored fortnightly on the samples for six consecutive months under the different storage conditions. Free fatty acid and calcium levels were determined according to the procedures of Pearson (1985). Proximate and gross energy were determined according to AOAC (1980), and phosphorus was colorimetrically determined following the quinol/sodium sulphite method (Yuen and Pollard 1955).

Statistical analysis

Data was analyzed by ANOVA using the GLM procedure of SPSS for windows (version 10.0) and LSD was used to determine differences between means (SAS 1989). Differences were considered significant at P < 0.05.

Results  

The nutrient composition of the samples is presented in Table 1.

Cocoa-cake-with-shell (CCWS) had the least moisture content with PKC having the highest. Ether extract and free fatty acids also followed a similar trend as the moisture content whilst crude protein content followed the reverse trend of the moisture content with CCWS having the highest crude protein content and PKC having the least crude protein content (Table 1).

The effect of storage conditions on the chemical composition of the three oil seed cakes is given in Table 2.

The moisture, crude protein, free fatty acids, total carbohydrates, gross energy, mineral ash, calcium and phosphorus contents of CC and CCWS did not significantly (P> 0.0 5) differ under the four storage conditions. The situation was different when the moisture levels in PKC are considered. This showed significant variations over time (P<0.03). The moisture content of PKC was the least under deep freezer (DF) conditions compared to the other storage conditions. Consequently the dry matter content was highest under DF conditions compared to the other storage conditions (Table 2). The mean moisture levels in the three samples ranged between 4.69 – 5.35% (CCWS), 5.42 – 5.98% (CC) and 5.93 – 6.96% (PKC). Under room temperature (RT) the levels of free fatty acids significantly increased compared to storage under air conditioning (AC) and refrigeration (REF). Ether extract was highest under DF for CC and PKC whilst the same was highest under AC for CCWS (Table 2).

The pattern of change for the various nutrients in the three oil seed cakes is represented in Figures 1 – 3. There was a general rise in the moisture and FFA contents of CCWS over the storage period. However whilst the increase in the moisture content was gradual  that of the FFA showed sharp increases under all the three  storage conditions. The moisture content of CCWS under RT dropped after week 16, whilst under DF moisture content shot up after week 18. Ether extract on the other hand, decreased over time whilst crude protein stayed fairly constant over the entire storage period.

Apart from the moisture content under DF which showed a sharp drop during week 4 of storage, moisture content, ether extract and crude protein contents of PKC stayed fairly the same over the entire storage period under all three storage conditions. There was a sharp drop in the crude protein content of the sample under DF storage during week 18 which bounced back at week 10 (Figures 2). On the other hand, the FFA content showed a consistent rise under all storage conditions, with the rise being more prominent under RT.. 

Figure 3 indicates that the moisture and ether extract contents of copra cake showed wide fluctuations over the storage period under all three storage conditions. The moisture content showed the widest fluctuations under RT with ether extract content showing the widest fluctuations under DF storage. Generally, the ether extract content declined over the storage period under all three conditions. The crude protein content, on the other hand, was fairly constant over the entire period of storage for all three conditions. With the exception of a sharp rise during week 10 under AC storage, the FFA content showed a gradual rise over the entire storage period with the rise under RT showing the highest increases whilst the rise under DF showed the lowest increases.   

Discussion 

The moisture contents in the three oil seed cakes were lower than the safest limit of 12 – 14% above which fungal growth is most probable (Crampton and Harris 1969, Bala 1979). The moisture levels in all the samples under all the storage conditions would, therefore, not encourage rapid deterioration though the possibility of ketonic rancidity cannot be ruled out (Pearson 1985). The moisture levels in CC and CCWS do not conform to the situation when a fermented soybean product (soyiru) was stored for 14 days under refrigeration and ambient temperatures (Kolapo and Sanni 2007). Kolapo and Sanni (2007) reported increases in the moisture levels of soyiru under refrigeration and ambient temperatures which they attributed to greater microbiological activities. According to Frazier and Westhoff (1978), elevated moisture levels in feed samples during storage due to growth of microorganisms is as a result of changes in the level of available moisture by the release of metabolic water or by the alteration of substrates so as to free water.

The crude protein content of the samples were not significantly altered under the four storage conditions during the entire six month period (P > 0.05). The mean crude protein levels obtained in the present study corroborates reports made by Collingwood (1958) to the effect that crude protein levels in oil seed cakes are not affected by storage conditions. The same observation, however, contradicts reports by Kolapo and Sanni (2007) which indicated that storage of soyiru for 14 days under refrigeration and ambient temperature conditions resulted in decreased proximate parameters.

The apparent contradictions in these reports could be due to differences in the chemical compositions of the samples. Tomassi (1988) and Kolapo and Sanni (2007) have indicated that various chemical and enzymatic reactions  in the composition of foods or feeds such as the presence of double bonds in unsaturated lipids render them more susceptible to oxidation and thus affect their acceptability, shelf life and safety. Thus, oils with relatively high degree of unsaturations would be more susceptible to fatty acid oxidation and hence rancidity than those with saturated fatty acid. Consequently the fatty acid composition of fats/oil among other factors, determine its keeping quality as well as shelf life.

Fats/oils usually tend to undergo changes which results in the generation of unpleasant taste and odour during storage and the concentration of FFA plays a key role in such adverse changes (Pearson 1985). In this regard, Wilson and McDonald (1986) reported that peroxidative changes in polyunsaturated fatty acids have been associated with the aging of oil seeds such as soybean. In this study the different storage conditions as well as duration of storage did not, however, significantly influence the ether extract levels in all three oil seed cakes within the period of storage (P > 0.05). However, compared to the initial levels (Table 1), the free fatty acid levels were significantly higher after the fifth month of storage period regardless of the oil seed cake and conditions of storage (P < 0.05). The FFA levels obtained in this study grossly contrast that reported by Iwe (1991) and Kolapo and Sanni (2007) whilst agreeing with results obtained from studies on stored sunflower oil (Zia-ur-Rehman et al 2003).

Increased FFA level apart from impacting unpleasant taste and odour to feed, also affect the nutritive value of the feed. This has been ascribed to the formation of chemical complexes with proteins leading to denaturation, decreased feed intake, and development of undesirable toughening of tissues as well as the reduction of water holding capacity (Ihekoronye and Ngoddy 1985, Pearson 1985).

This study indicates that the period of keeping copra cake (CC) under AC and RT conditions should not exceed 6 weeks beyond which free fatty acid level would increase above the recommended level of 1.50% which becomes indicative of the onset of rancidity (Pearson 1985).The results further indicated that CC could be stored under refrigeration (REF) and deep freezer (DF) for 6 and 8 weeks respectively without deterioration based on the FFA levels. It was observed that cocoa-cake-with-shell (CCWS) may not be stored longer than 2 weeks under ambient temperature condition (RT). Moreover, palm kernel cake (PKC) could be stored under deep freezer (DF) condition and remain wholesome up to 10 weeks. On the other hand, storage under RT was found not to be a good storage measure for PKC and it should not go beyond the first two weeks.

Conclusions 

• The study demonstrated that the nutrient levels did not significantly vary when copra cake (CC), palm kernel cake and cocoa-cake-with-shell (CCWS) were considered. Albeit, the FFA levels markedly differed relative to the initial levels regardless of the oil seed cake. The free fatty acid levels in CCWS indicated that it should not be kept longer than 2 weeks when stored under room temperature (RT). Copra cake on the other hand, may be stored up to 6 and 8 weeks under refrigeration (REF) and deep freezer (DF) respectively. PKC had significant changes in FFA under the four storage conditions particularly under RT. Deep freezing (DF) was observed to be the best means of storing PKC while room temperature (RT) was the poorest.

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Received 2 December 2009; Accepted 22 December 2009; Published 7 February 2010

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