Asian J. Dairy & Food Res, 36(3) 2017 : 260-263
AGRICULTURAL RESEARCH COMMUNICATION CENTRE
Print ISSN:0971-4456 / Online ISSN:0976-0563
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Effect of different drying and grinding methods on biochemical properties of sweet orange peel powder K.B. Sankalpa*, C.T. Ramachandra, B.L. Dinesha, Uday Kumar Nidoni, Sharanagouda Hiregoudar and R.V. Beladhadi Department of Processing and Food Engineering, College of Agricultural Engineering, University of Agricultural Sciences, Raichur-584 104, Karnataka, India. Received: 27-03-2017 Accepted: 20-05-2017 DOI:10.18805/ajdfr.v36i03.8975 ABSTRACT Sweet orange (Citrus sinensis Osbeck) belongs to sub family Aurantoideae which is categorised under family Rutaceae. Peel is the main by-product obtained from sweet orange fruit juice processing industry. Peel is rich in many bioactive component, so to utilize this peel for industrial purpose it need to cover to stable form. So in present study sweet orange peel is dried in three drying technique: solar tunnel drying, hot air drying and dehumidified air drying and ground with three different grinding methods: hammer mill grinding at ambient temperature, hammer mill grinding with water cooling and hammer mill grinding with liquid nitrogen cooling. Ground sweet orange peel powder was examined for functional properties. Among nine combinations, dehumidified air dried and liquid nitrogen (LN2) cooled ground sample showed significantly good functional properties such as ascorbic acid (40.00 mg.100g-1), phenols (2.23 mg.g-1), total carotenoids (0.28 mg.g-1), total flavonoids (33.76 mg.g-1), radical scavenging activity (75.59 %), pH (6.26) and water activity (0.35). Key words: Biochemical properties, Dehumidified air drying, LN2 cooling grinding, Sweet orange peel powder. INTRODUCTION Peel is the main by-product obtained from sweet orange fruit juice processing industry and it is highly perishable, if not processed the peel become waste and in turn may become a possible source of environmental pollution By-product recovery from fruit wastes can improve the overall economics of processing units and the problem of environmental pollution also can be reduced considerably (Kumar et al., 2011). Around the world, 31200 tonne of orange and other citrus fruits are annually processed out of which the estimated annual waste is 15.6 million MT (Djilas, 2009). These are mainly used for animal feeds, due to their high fibre content; they could represent an interesting source of dietary fibre (Larrauri et al., 1997). The sweet orange peel is rich source of dietary fibre but dietary fibre are not only desirable for nutritional value but also for its functional properties (Marin et al., 2007). In addition, citrus peel is interesting source of phenolic compound and found to have good total radical antioxidative potential (Chen et al., 2012)
of dried peel. Solar tunnel drying is improved method over the open yard sun drying since results in short drying time and safer product. Nowadays hot air drying is quite common in many industries due to easy of operation, low investment and operation cost compare to other advanced technique. Dehumidified air drying is one of the improved drying method which dries the sample with relatively less temperature and humidity. The main aim of grinding of sweet orange peel slices is to obtain smaller particle size with good product quality in terms of functional properties. In the ambient grinding process heat is generated when energy is used to fracture a particle into a smaller size. This generates heat which is detrimental to the product and results in loss of quality. Hence, the produced heat can be reduced by circulating the water and in another method by supplying liquid nitrogen to milling chamber. This work it describes the comparative study on three drying and three grinding methods on biochemical properties of sweet orange peel powder.
Many experimental investigations have been carried out on fibre content (Larrauri, 1999; Garau et al., 2007; Lario et al., 2004; Peerajith et al., 2012), flavonoids, carotenoids and phenol content of sweet orange peel (Wang et al., 2007; Agocs et al., 2007), but there are no extensive studies conducted on the conversion of sweet orange peel in to powder. Conversion of fresh peel in to powder involves two important steps: drying of sweet orange peel and grinding
MATERIALS AND METHODS Sample preparation: Fresh sweet orange (cv. Sathgudi) were selected uniformly according to harvest, color, size and freshness. The fruits were washed, weighed, peeled by using knife and were cut into small pieces (10 to 20mm), after that there were washed using hot water at 90 °C for 5 min. After that peel surface moisture was removed then it was followed by three drying methods: solar tunnel drying (STD), hot air
*Corresponding author’s e-mail:
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Volume 36 Issue 3, 2017 drying (HD) and dehumidified air drying (DD) and three grinding methods: hammer mill grinding at ambient temperature (AT), hammer mill grinding with water cooling (WC) and hammer mill grinding with LN2 cooling (LN). After the grinding, powder was passed through a 212-m sieve to get uniform particle size. Biochemical properties Ascorbic acid: Vitamin C content was estimated according to method described Sadashivam and Manickam (1992). Determination of vitamin C content of samples was carried out thrice and the average value was considered as vitamin C content of powdered sweet orange peel. Total carotenoids and total flavonoids: Total carotenoid and total flavonoids quantitation was carried out according to method described by Wang et al. (2007) and was expressed as â-carotene equivalents and rutin equivalents, respectively. Phenolics: Total phenolic content of samples were determined by using the Folin–Ciocalteau reagent (FCR) according to method described by Ahmad and Langrish (2012). Catechol was used as an equivalent standard. Standard curve of catechol was used to estimate concentration of phenols. Radical scavenging activity: DPPH (2,2-diphenyl-1picrylhydrazyl) radical scavenging activity was determined according to El-aal and Halaweish (2009). pH: The pH of sweet orange peel powder was measured according to procedure in bibliography (Lario et al., 2004) by using digital pH meter (make: Systronics; model: 361). Water activity: The water activity of sweet orange peel powder was measured by Rotronic Hygrolab water activity analyzer (Reddy et al., 2014).
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All the experiments in the study were conducted in triplicate. Factorial completely randomised design (FCRD) was used to analyse the data. The experimental design was done with the aid of the Design-Expert software version 7.7.0 (Statease Inc., Minneapolis, USA) to know the best combination among the three drying methods and three grinding methods. RESULTS AND DISCUSSION Ascorbic acid: Sweet orange peel powder obtained by dehumidified air drying and hammer mill grinding with LN2 cooling had significantly higher ascorbic acid content of 40.00 mg.100 g-1 compared to all other treatments. Solar tunnel drying and ambient temperature grinding method gave significantly lowest ascorbic acid content of 18.33 mg.100g-1. In this case both drying, grinding and interaction had significant (p < 0.05) effect on the ascorbic acid content. The results of ascorbic content in sweet orange peel powder in the present study was in agreement with the value of 59.6±5.2 mg.g-1 in peel of citrus fruit (Lopez et al., 2004; Barros et al., 2012). Ascorbic acid degradation describes the vitamin C loss in drying and grinding process, degradation of vitamin C increased with increase in drying air temperature and drying period, so vitamin C content of sweet orange peel powder dried in dehumidified air dryer and grinding with LN2 was found to be more than those obtained using other drying and grinding method (Kaya et al., 2010). Amount of ascorbic acid present in sweet orange peel powder obtained from different drying and grinding combination is given in Table 1. Total Carotenoids: Total carotinoid content was significantly (p < 0.05) affected by drying methods, grinding
Table 1: Effect of three drying and grinding methods on proximate composition and functional properties of sweet orange peel powder Drying Grinding Ascorbic acid pH Water Total Total Phenolics RSA(%) method method (mg.100g -1) activity flavonoid carotenoids (mg.g -1) (mg.g-1) (mg.g-1) STD AT 18.33 5.89 0.44 22.28 0.18 1.51 64.70 WC 21 5.91 0.41 25.85 0.19 1.71 66.50 LN 23.33 5.94 0.39 26.22 0.23 1.84 67.15 HD AT 21.33 5.98 0.4 24.47 0.18 1.71 65.01 WC 25.66 6.12 0.41 26.05 0.19 1.95 68.27 LN 26.99 6.2 0.37 26.60 0.22 2.00 72.18 DD AT 32.3 6.04 0.4 29.72 0.20 1.83 72.38 WC 34 6.19 0.39 31.74 0.24 2.08 73.13 LN 40 6.26 0.35 33.72 0.28 2.23 75.59 Std. Dev. 0.66 0.14 0.020 0.88 0.0081 0.075 0.89 C. V (%) 2.46 2.38 5.06 3.22 0.21 4.00 1.28 R2 0.993 0.55 0.696 0.957 0.955 0.918 0.962 p value < 0.0001
