Original Article Effect of Drying Method on Spearmint (Mentha spicata var. Viridis L.) Oil Content and Physicochemical Properties El Rasheed Ahmed Salim*1, Abu-Bakr Ali Abu-Goukh2, Hassan El-Subiki Khalid3 and Gaffar Mohamed El Hassan4 1Food Industry Department, Industrial Research & Consultancy Centre, Ministry of Industry, Sudan 2&4Department of Horticulture, Faculty of Agriculture, University of Khartoum, Sudan 3Medicinal and Aromatic Plants Institute, National Centre for Research, MOST, Sudan ABSTRACT The experiment was investigated the effect of drying method of spearmint oil content and physicochemical properties. Spearmint samples were dried under different conditions till the weight of herb in each reached 20%. The treatments were: (i) shade drying under ambient conditions, (ii) sun drying (iii) forced-air oven drying at Address for 60oC, (iv) forced-air drying at 70oC and (v) forced-air oven drying at o Correspondence 80 C. Oil was extracted by water distillation according to the technique of the British Pharmacopoeia. Physicochemical properties Food Industry were determined according to British Standards Institute. Spearmint Department, Industrial oil content was significantly higher in shade drying than in sun Research & drying and in forced-air oven drying. Oil content decreased with an Consultancy Centre, increase in oven temperature. Refractive index and acid value were Ministry of Industry, significantly higher in shade drying, compared with sun drying and Sudan. decreased with an increase in oven temperature in forced air drying. E-mail: Ester value of spearmint oil followed a trend, but opposite to that of rasheedahmedsalim acid value. @hotmail.com Keywords: Spearmint, Sun drying, Oven drying, Shade drying. INTRODUCTION Mint group (Menta spp) is products are widely used as spice, flavoring considered as one of the most important and agent and in folk medicine3,4. The oil is used valuable essential oil source [1]. Spearmint is in pharmaceutical, anti-septic, perfumery cultivated in different parts of the world, for and food industries3,5. example in North American, England, The major commercial form of Germany, Holand and in the Mediterranean spearmint is still the self-stable dried region1. Minor cultivation areas of spearmint product, since it can be transported easily exist in China and India, where high quality and stored well under proper conditions6. oils are produced2. The mint plants and their During the drying process, the condition or American Journal of Phytomedicine and Clinical Therapeutics www.ajpct.org Salim et al__________________________________________________ ISSN 2321 – 2748 quality of spearmint oil can be adversely removed immediately from the harvested affected. It can result in loss of essential oils, spearmint material. changes in color and texture and decrease in nutritive value7,8. The drying method and Experimental design duration have highly significant effects on The experiment was laid out in a oil content and composition. Essential oils completely randomized design, with four are retained to a greater extent when plants replications. The treatments were: (i) Shade are dried under ambient conditions, drying, (ii) Sun drying, (iii) Forced-air oven compared to sun drying or forced air9. drying at 600C, (iv) Forced-air oven drying Essential oil composition and quality are at 700C and (v) Forced-air oven drying at greatly influenced by oven drying 800C. temperature. About 75.7% of essential oils are lost during oven drying at 60oC than at Drying 30oC10. As the temperature increases, the The different spearmint samples monoterpenes content gradually decreases were dried under the following conditions and sesquiterpenes content increases11. till the weight of herb in each reached 20% The aim of this study was to evaluate of total weight: (a) Shade drying: samples the effect of drying method of spearmint were dried under shade at ambient herb on oil content, composition and temperature (370C) by spreading the physicochemical properties of the oil. spearmint herbs on polyethylene sheets. (b) Sun drying: samples were dried under direct MATERIALS AND METHODS sunshine for six days (144 hours) on polyethylene sheets. The herbs were turned Experimental site twice a day to expose the inner layers to A field experiment was conducted at direct sun for regular drying. (c) Air-forced ‘Halfaya’ area, Khartoum North (150 40/N, 0 / drying: samples were immediately dried in a 32 22 E). forced-air oven (Memmert 854 Schwabach – Karl Kollo Scientific Technical supplies, Experimental Material West Germany) under controlled Spearmint (Mentha spicata var. temperature either at 600C (for 14 hours), Viridis) plants were raised from 700C (for 12 hours) or 800C (for 10 hours). underground runners (rhizome-like After drying the herb samples were allowed rootstock), obtained from fully mature plants to cool and placed in the black polyethylene grown in a spearmint growing area at bag for further investigations. ‘Halfaya’, Khartoum North. The underground and surface runners were Oil extraction and determination transplanted into new well prepared flat beds The spearmint oil was extracted by at 30 x 30 cm Spacing. Pre-transplanting water distillation and determined according irrigation was applied, followed by the first to the technique of British Pharmacopoeia12. irrigation immediately after transplanting. 7 After distillation to be completed, the whole Irrigation was carried out every . system was left for about half an hour, so Samples of herb, about two that a good separation can be obtained. The kilograms each, were harvested from well volume of the oil was recorded and established 70 days plants. The aerial parts expressed in ml per 100 g. of the plant, (main aerial stem, branches and leaves) were cut about 5 cm above the ground. Foreign materials and weeds were AJPCT[3][06][2015] 487-493 Salim et al__________________________________________________ ISSN 2321 – 2748 Physicochemical properties 76% of essential oil was lost during oven- The oil was prepared for drying of Lavandin (Lavandula intermedia) at examination according to British Standards 60oC, compared with drying at 30oC10. Deans 2073: 1976 (BSI, 1976)13. Refractive index and Svoboda16 mentioned that loss of was determined by Abbe refractometer (No. essential oil is unavoidable during drying 918095-Bellingham and Stanley Ltd., processes, but selection of the best drying London, England) according to British parameters helps to minimize any loss of the standards Institute13 and expected to four oil during drying. decimal places. Acid value and ester values were determined according to British Effect on physicochemical properties of Standards13. The acid value was expressed spearmint oil in mg of KOH per g spearmint oil and ester In the natural herb drying, refractive value was expressed in mg of KOH required index of spearmint oil was higher in oil to neutralize the acid per g spearmint oil. distilled from herbs dried under shade at ambient temperature (1.486) than that from Statistical analysis sun-dried herbs (1.484) (Fig. 2). In the forced- Analysis of variance and Duncan air oven drying, refractive index was highest multiple range test with a significance level in oil extracted from herbs, dried at 60oC of P ≤ 0.05 was performed on the data14. (1.488), followed by the herb, dried at 70oC (1.487) and least in the herbs dried at 80oC RESULTS AND DISCUSSION (1.481) (Fig. 2). Acid value was higher in spearmint Effect on spearmint oil content oil from herbs, dried under shade at ambient Oil content was highest in both temperature (1.403), compared to that from shades dried herbs (at ambient temperature) o herbs dried under direct sunshine (1.122) and oven-dried herbs at 60 C (1.1 ml/100g), (Fig. 3). followed by sun-dried samples (1.0 In a forced - air oven drying, acid ml/100g), then in oven-dried samples at value was higher in oil from forced-air dried 70oC (0.8 ml) and least in oven-dried herb at 60oC (3.366), followed by that dried at samples at 80oC (0.6 ml/100g) (Fig. 1). o o 9 70 C (3.039), and least in that dried at 80 C Charles et al. reported that the drying (1.683) (Fig. 3). Ester values of spearmint oil method and duration have highly significant followed a trend just reverse to that of acid effects on oil content and composition. values. In natural herb drying, ester value was Artemisinin content in Artemisia annua L. higher in oil from the sun-dried samples (Asteraceae) was retained to a greater extent (111.21) than from those dried under shade when plants were dried under ambient (84.15) (Fig. 4). In a forced - air oven drying, temperature, compared to sun-drying or ester value was low in oil from herbs, dried at forced-air at 300 to 80oC9. Diaz-Maroto et o o 15 60 C (50.49), followed by those dried at 70 C al. evaluated the effect of drying method on (36.00) and highest in herbs dried at 80oC volatile compounds content, structural (28.05) (Fig. 4). During the drying process, integrity and sensory characteristics of the condition, properties and quality of parsley. Conventional oven-drying resulted in spearmint oil can be adversely affected7,8. losses of volatile compounds that fluctuated Essential oil composition and quality are with the drying temperature and drying time o significantly influenced by oven drying employed. Oven-drying at 45 C and air- temperature10. Hot air drying, in some case, drying at ambient temperature where the can cause changes in oil properties and method produced the best results is that about AJPCT[3][06][2015] 487-493 Salim et al__________________________________________________ ISSN 2321 – 2748 degradation in terms of color reaction and Medicinal and Aromatic Plants Institute decomposition of active ingredients17. Due to (NCR, Sudan), Department of Food Research the drying conditions, the rate of loss of Industries at (IRCC, Sudan), Mr. Mohammed different oil components may be different. Damona in Pharmaceutical Industries (IRCC) Lighter oil components may be evaporate for their generous help in conducting at higher rates than the heavier components18.