Phytonutrients in citrus fruit peel meal and nutritional implication for livestock production

O I A Oluremi, J Ngi and I A Andrew

University of Agriculture, Makurdi.Benue State. Nigeria
biyi1oluremi@yahoo.com

Abstract

The peels of four varieties of citrus fruits namely Citrus sinensis (Washington), Citrus sinensis (Ibadan), Citrus limonum and Citrus qurantifolia were sun-dried and milled to obtain citrus fruit peel meal (CFPM). The CFPM of each variety was subjected to phytochemical screening to detect the presence of phytonutrients.

Phytochemical screening showed that each of the peels contained tannin, saponin, phytate, oxalate, flavonoids and limonene. Whereas, the variation of each of these phytonutrients between the peel meals was significantly different (p<0.01) except for tannin (p>0.05), they were at low concentrations and below the levels reported in literature to be toxic to livestock species.

Animal studies are however recommended to determine at what level limonene becomes toxic to farm animals.

Keywords: Citrus fruit peel, livestock production, phytonutrients

Introduction

The shortage of good quality feeds needed to sustain livestock growth, especially during the dry season has been a major challenge to the industry in the developing countries. Thus crop residues, agro-industrial by products and non conventional feed resources which abound during the dry season are being evaluated to access their nutritive potential to support livestock productivity. Several factors have been generally identified as limiting to the utilization or high incorporation of non conventional feedstuffs in livestock feed. These include low protein content (Gohl 1981), high fibre (McDonald et al 1988), amino acid imbalance and presence of anti-nutritional factors (Tacon and Jackson 1985). Anti-nutritional factors have significant negative effects on livestock production. These effects include reduction in palatability, digestibility and utilization of ration, intoxication of different classes of livestock, resulting in mortality or decreased production of animal and reduction in the quality of meat, egg, and milk products due to the presence of hazardous residues (Amuchie 2001).

A number of agro-industrial by-products or wastes like citrus pulp, citrus meals, citrus seed meal, citrus molasses and citrus peels are generated from fresh citrus after the main products of interest have been removed or extracted during processing or peeled for direct human consumption as in the case of developing countries. Clusters of peel of the sweet orange are usually noticed on streets and along major roads in Nigeria because government and orange retailers have no strategic disposal programme thus becoming an environmental problem. Ipinjolu (2000) has suggested that rather than discarding the orange peels, they can be sun-dried and then milled in grinding machine to fine particle to obtain the orange peel meal which can be included in fish diets. Sweet orange fruit rind (peel) meal has been observed to be a source of calorie and protein comparable with maize (Oluremi et al 2006). The peel contains oil sacs and the oil is composed of 91-94% d-limonene and 2.0-2.1% β-myrcene as a minor constituent (Arizona Chemical 1999). Polymetholated flavones are also a class of compounds found in citrus peel and produce no negative side effects in the animals fed the polymetholated flavones containing diets (Davis 2004). The objective of this study is to determine the phytonutrients in the peel of some common varieties of citrus and to show their dietary implication in livestock production.
 

Materials and methods

Four varieties of citrus fruit namely Citrus sinensis: Washington variety (CSW), Citrus sinesis: Ibadan varieties (CSI), which are both sweet orange varieties, Citrus limonum: Lemon (CL) and Citrus qurantifolia: lime (CQ) were purchased from the wholesale citrus fruits depot in the University town of Makurdi. The outer cover of the fruits otherwise called flavedo which contains chromoplasts and oil sacs were carefully peeled to minimise the inclusion of albedo which is an inner layer of spongy white tissue. The peels obtained from each of the four citrus fruits were sun-dried until they become crispy, a process which took 48 hrs for Citrus sinensis (Washington), Citrus sinensis (Ibadan) and Citrus qurantifolia and 72hrs for Citrus limonum. Dried peels were ground with a Hammer Milling machine having a screening sieve of 1mm pores to obtain the citrus fruit peel meal (CFPM). Homogenous sample of each of the peel meals of the Washington variety (CSWM), Ibadan variety (CSIM), lime (CLM) and lemon (CQM) the four citrus fruits was subjected to phyto-chemical analysis for qualitative and quantitative determinations of phytonutrients (Harborne 1973; Sofowora 1993 and Trease and Evans 1989). The quantitative data obtained was statistically analysed using one way Analysis of Variance described in the Minitab Statistical Software (1991).
 

Results and discussion

The phytochemical screening of the citrus fruit peel meal samples revealed the presence of limonene, tannin, saponin, phytate, oxalate and flavonoid in all the citrus fruit peel meals (Table 1).

The level of each of these compounds was highly significantly different (p<0.01) between the peel meals of the different citrus fruits with the exception of tannin which did not differ significantly (p>0.05) as shown in Table 2. It was also observed that the levels of saponin, phytate oxalate and flavonoid in the peels were significantly higher (P<0.01) in the two sweet orange varieties (Washington and Ibadan) than in CLM and CQM.

Tannin which usually gives rise to a dry, pickery, astringent sensation in the mouth was in the range of 0.433-0.523% in the citrus fruit peel meals. This is lower than 1-20% commonly found in cereals and legumes reported to have depressed the growth rate, resulted in a poor feed efficiency ratio and increased the amount of food required per unit weight gain in non-ruminants (Price and Butler 1980). However, in ruminants, dietary condensed tannins of 2-3% have been shown to impart beneficial effects because they reduce the wasteful protein degradation in the rumen by the formation of a protein tannin complex (Barry 1987).

The concentration of saponin in the peels of the citrus fruits was between 0.030 and 0.043%. Saponins are bitter and reduce the palatability of livestock feeds. Among the effects of saponin on animals are growth inhibitions in swine and poultry, reduced palatability of food and in increased excretion of cholesterol concentration (Malinow et al 1987). The saponin content of the peel meals were observed to be appreciably below 3% which was reported by Kumar (1991) to be responsible for cattle losses when they grazed on alfonibrilla (Drymaria arenaroides) and thus may not be hazardous to livestock.

The level of phytate in the peels of the citrus fruits range between 0.062 and 0.082%. This is observed to be low when compared with phytate content of 146 and 353mg % in maize, 206 and 280mg% in sorghum, 14mg % in potato (Concon 1988), 624mg %, 855mg % and 637mg % in cassava, cocoyam and yam, respectively (Marfo and Oke 1988). Phytate presence is largely blamed for the complexing of dietary essential minerals in legumes and cereals and rendering them poorly available to monogastric animals. It is apparent that phytate content of the citrus fruits peel meals is safe for livestock consumption.

Oxalate was detected in the citrus fruit peel meal and its concentration was between 0.033 and 0.048%. Like phytate, oxalate can decrease the availability of dietary essential minerals such as Ca. At high concentrations, oxalate causes death in animals due to its corrosive effects (Kumar 1991). In small amounts, it causes a variety of pathological disorders including hyperoxaluria, pyridoxine deficiency, and calcium oxalate stones. The oxalate level in CFPM seems low when compared with 0.7%, 0.275% for cocoa and beet roots, respectively (Gontzea and Surtzescu 1968; Concon 1988).

Flavonoids were detected in citrus fruits peel meals with phytochemical screening. Quantitatively, the amount present was between 0.025 and 0.045%. Flavonoids have been reported to function as pigments and antioxidants (Kumar 1991) and can inhibit enzymes in mammals (Hollman 1997). The most important flavonone in oranges is hesperidin which has been reported to lower high blood pressure as well as cholesterol in animal studies and have strong anti-inflammatory properties (CSIRO 2004).

The level of limonene found in citrus fruits peel meals was in the range of 1.240 - 1.555%. Citrus seed meal has been reported to contain limonene which is toxic to pig and especially to poultry (Serres 1999). While orange peel has been included in the diet of ruminant especially in those areas where its production is high (Megias et al 1993), the presence of limonene may be a limitation to its use in raising monogastric animals. Thus far, nutritional trials with monogastric animals have shown that the meal of sun dried peels of Citrus sinensis can replace dietary maize in broiler diet up to 20% (Agu 2006), and 40% in rabbit (Oluremi et al 2005), without any adverse effect on their performance.
 

Conclusions

• Nutrition quality of feeds is critical in livestock development. The phytochemical examination of citrus fruits peel meals of Citrus sinensis (Washington variety), Citrus sinensis (Ibadan variety), Citrus limonum and Citrus qurantifolia has shown that they contain tannin, and saponin, phytate, oxalate, flavonoid and limonene in varying highly significant amounts (p<0.01). It was observed that their concentrations in CFPM were lower than the levels at which these chemical compounds have been reported be harmful to farm animals.

• The effect the presence of limonene which has been reported to be toxic to pig and especially poultry should be investigated to determine at what level it becomes toxic to various livestock species.
   

References

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Received 22 April 2007; Accepted 6 May 2007; Published 6 July 2007

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