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TEXTURAL PROFILE ANALYSIS AND PHENOLIC CONTENT OF SOME DATE PALM VARIETIES

Muhammad Nadeem, Salim-ur-Rehman, Faqir Muhammad Anjum*

and Ijaz Ahmad Bhatti**

ABSTRACT A study was carried out in the Post Graduate Laboratory, National Institute of Food Science and Technology, University of Agriculture, Faisalabad during the year 2010. Twenty one date palm (Phoenix dactylifera L.) varieties were investigated at tamr stage for their physical characteristics, textural profile analysis and total phenolic content. Significant differences were recorded in the physical characteristics, textural profile and total phenolic content among varieties. Maximum fruit weight (13.89g), flesh weight (12.89g), fruit length (4.56cm) and volume (11.94cm3) were recorded in Dhakki. Edible/non-edible ratio of different date varieties ranged from 1.94 (Desi simple) to 14.50 (Aseel Sindh). Maximum water activity was found in Desi basray (0.482) and minimum in Karblain (0.323). The highest peak force of puncture test as an index of hardness during textural profile analysis was recorded in Dora (59.64g) and maximum value of fruit colour was observed in Desi red small (149.10CTn). Phenolic content ranged from 296.67 to 140.67mg (GAE) /100g fresh fruit weight. The results conclude that Dhakki, Aseel Sindh and Hillavi are suitable for table purpose while other varieties are suitable for processing and converting into date products.

KEYWORDS: Phoenix dactylifera; cultivars; chemicophysical properties;

phenolic content; Pakistan.

INTRODUCTION

Date (Phoenix dactylifera L.) plays an important role in the diet of natives of date growing regions due to high nutritional, health and economic values in addition to its aesthetic and environmental benefits (4). There are more than 150 varieties of date palm produced in Pakistan, among these the important varieties are Dhakki, Aseel, Zahidi, Fasli, Begum-jangi, Mojati, Karblain, Dora, Shungust, Choharay, Desi, Dagh, Gogna, Tota, Karwan, Halavi and

*National Institute of Food Science and Technology, **Department of Chemistry and Biochemistry, University of Agriculture, Faisalabad, Pakistan.

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Khudravi. Pakistan is among the top ten date producing countries. Its production was 557.5 thousand tons from an area of 90.1 thousand hectares during the year 2007-08 (6). Date flesh provides 73.5g carbohydrates, 2.3g proteins, 1.5g ash and 0.2g fat per 100g. It contains palmitoleic, oleic, linoleic and linolenic acids. It also provides vitamin A, C, B1, B2, folic acid and nicotinic acid and at least 15 mineral elements. The chemical composition of dates is variable due to various factors such as variety, region, climate, amount of fertilization and type of cultural practices (4). Dates are a rich source of antioxidents, mainly carotenoids and phenolics (2). These have more total phenolics as compared to other dried fruit. The antioxidant property of date varies depending upon the contents of phenolic components, vitamin C and E, carotenoids and flavonoids. The average contents of phenolics range from 193.7mg/100 g for fresh dates to 239.4 mg/100 g for dried dates. Phenolics increase after drying of some date varieties. It is actually due to the degradation of tannins by heat and maturation of enzymes during the drying process which leads to the release of phenolic compounds (12). Besbes et al. (11) observed significant differences in total phenolic contents in dried fruit of different varieties (11). Difference in phenolic compounds could be due to various factors such as variety, growing conditions, maturity, season, geographic origin, fertilizer, soil type, storage conditions, amount of sunlight received, cultural methods, process and stabilization conditions, climatic conditions, use of different analytical methods and use of different phenolic acid standards (1). Due to richness in phenolic compounds these are considered a valuable source of natural antioxidants that may have many health benefits for human (10). Fibre and calcium in dates play critical role in preventing heart diseases and colon cancer. Dates contain fructose which is better utilized as source of energy by diabetic patients than glucose and sucrose. Dates provide about 180 kcal/l00g. Dates are fat, sodium and cholesterol free and ideal ingredient for the quality product demanded by today's health conscious consumers (8). However, Ismail et al. (14) studied date consumption among different age groups and noted that younger population does not consume dates as much as the older population. So dates can be used to produce a product with enhanced nutritional quality and acceptability for consumers (3). Dates are used in different food items like date syrup, jam, frosts, fruit cake, salami-like rolls, date yogurt, vinegar, date muffins and biscuits, etc. (20).

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Low grade dates and date pits are used as animal feed. Dehydrated dates are used in the preparation of sweets, snacks, confectionary, bakery products and health foods (25). Polysaccharide material from dates has been used as a functional food and a source of active component in the development of drugs (17). These have also been identified as having antioxidant and antimutagenic properties and help control cardiovascular diseases due to the presence of dietary fibre (24). The physical properties of date varieties were studied by many scientists in different countries of the world (5, 7, 14, 18, 19). Ramadan (18) reported the flesh weight of different date varieties in the range of 3.43 to 7.30g, pit weight 0.86 to 1.40g, edible/non-edible ratio 3.90 to 5.22 and flesh weight in the range of 79.58 to 83.91 percent. Al-Shahib and Marshal (5) reported fruit weight from 6.5 to 10.6g, fruit length in the range of 2.65 to 3.88cm and fruit diameter 1.72cm to 2.35 cm in five different varieties of dates. Tafti and Fooladi (23) found the fruit weight of 10.20g, fruit length 3.4cm, fruit width 2.1cm and fruit volume 8.6cm3. Ismail et al. (14) studied five different date varieties and found the weight ranging from 7.55 to 10.32g, length from 2.85 to 3.66cm, diameter from 2.05 to 2.36cm, volume 6.94 to 9.16mL and density from 1.09 to 1.15g/mL. Qualitative and quantitative evaluation of date fruits is helpful not only for consumers, particularly processors, but also for traders. Chemical composition relating to nutritional and health benefits are vital for consumers. Physical parameters are indices of maturity, shelf life are useful for sorting, grading and processing of dates. The present study was designed to study the physical characteristics, texture analysis and phenolic content of various date palm varieties for exploring the suitability of indigenous date varieties for date products.

MATERIALS AND METHODS This study was carried out in the Post Graduate Laboratory, National Institute of Food Science and Technology, University of Agriculture, Faisalabad during the year 2010. Twenty one commercially available date varieties (Karblain, Aseel, Zaidy, Dhakki, Dora, Shungust, Choharay, Khopra, Karbalai Sindh, Desi green, Desi basraywal, Desi simple, Desi red small, Desi black, Desi small, Desi basray, Dora basraywal, Dora desi, Simple basraywal, Aseel Sindh and Hillavi) were collected at tamr stage (full maturity stage ) from Date Palm Research Centre, Jhang and local market of different areas of

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Pakistan. Samples were selected randomly without any preference to size, shape, colour, appearance and firmness, and stored at 4°C. Analytical grade chemicals were purchased from Sigma Aldrich (Seelze, Germany) and Lab-Scan (Dublin, Ireland) available in the local market. Physical analysis Twenty fruits from each variety were selected randomly for physical measurements and each fruit represented one replicate. Fruit weight was recorded with top load balance. Length and diameter were measured with a micrometer caliper. Water displacement method was used to determine the fruit volume and density was recorded as weight over volume. After pitting, flesh and pit weights were recorded as described by Ismail et al. (14). Water activity of different date varieties was determined by using an electronic hygropalm water activity meter (Model Aw-Win, Rotronic, equipped with a Karl-Fast probe). Hygropalm water activity meter is a portable humidity temperature indicator, having 9 volts battery. Date varieties were analyzed according to Piga et al. (16) with some modifications. The colour values of different date varieties were determined with the help of coloure meter (Colour Test-II; Neuhaus Neotec). The colour meter was calibrated by using standards (54 CTn for dark and 151 CTn for light). The colour of date varieties was determined by placing the date samples under the photocell. Sample readings were compared with the standard. Texture analysis Texture of date varieties was determined according to Piga et al. (16) with some modifications by using a texture analyzer (Mod.TA-XT2 Stable Microsystems, Surrey, UK) with a 5kg load cell. The Texture Expert Program version 4.0.9.0 was used for data analysis. Textural determinations were made by using a 2mm needle probe for puncture test. Date samples were punctured to determine structural characteristics present inside or on the surface. Samples for puncture test were placed centrally on heavy duty plate form under the needle probe. Both the load cell and probe were calibrated before test. Hardness measurement of samples by puncturing involved plotting force (g) versus time (sec). Maximum force (g) was used as an index of hardness for the puncture test (Table 1).

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Table 1. TA-XT2 settings for comparison of hardness of different date varieties by penetration with a 2mm needle probe.

Model Measure force in compression Option Return to start Pre-test speed 1.0 mm/s Test speed 0.5 mm/s Post test speed 10.0 mm/s Distance 1 mm Trigger force Auto-5g Tare mode Auto Data acquisition rate 400pps

Total phenolic content Analysis for total phenols was carried out with UV spectrophotometer by Folin-Ciocalteu reagent method as described by Singleton et al. (21). Gallic acid (0.5g) was dissolved in 10mL ethanol and then diluted to 100mL with distilled water (5g/L). Stock solution of diluted 1, 2, 5, and 10mL to 100mL with deionized water to create standards with 50, 100, 250, and 500mg/liter concentrations, respectively. One gram of date sample was ground in 10mL 80 percent ethanol in pestle mortar. This homogenate was centrifuged at 10,000 rpm for 20 minutes. Supernatant was saved and residue was re-extracted with 80 percent ethanol, centrifuged and the supernatant was again recovered and evaporated to dryness. The residue was dissolved in 50mL deionized water and filtered through Whatman No.1 paper. 2.5mL of 0.2N Folin-Ciocalteu reagent was added to 0.5mL of this sample solution in test tube and after 5 minutes 2mL of 20% sodium carbonate (Na2CO3). The contents were mixed and incubated at room temperature for two hours. The absorbance was measured at 760nm against a reagent blank. Gallic acid was used to prepare standard curve. Three readings were used to express mean values of total phenolic content in mg of gallic acid. Statistical analysis The results obtained from each attribute were statistically processed using analysis of variance technique with the help of statistical package 8.1 by a significant T-test (p≤0.05), mean separation was done (p≤0.05) by using least significant test (22).

RESULTS AND DISCUSSION

Physical properties Data on fruit weight of different date varieties showed a significant (p ≤ 0.05) difference among varieties. Out of 21 dates varieties, Dhakki gave the

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heaviest fruit (13.89g) followed by Aseel Sindh (13.64g) (Table 2). The cultivars Choharay, Dora Basraywal and Hillavi had also good fruit weight i.e. 12.08, 11.87 and 11.72g, respectively, whereas the minimum fruit weight was observed in case of Desi simple (3.04g). Mean values for fruit weight of other varieties ranged from 4.60 to 11.62g. These results are close to the range reported by Al-Shahib and Marshal (5) in different date varieties. The data on stone weight also reflected significant (p ≤ 0.05) differences among date cultivars, ranging from 0.80g (Aseel) to 1.89g (Dora Basraywal). Hillavi (1.44g) and Desi basray (1.39) also showed better stone weight. However, the lowest mean value of stone weight was observed in Aseel (0.80g), Karblain (0.85g) and Aseel Sindh (0.90g). The highest mean value of stone weight percentage was found in Desi simple (34.20%) followed by Desi red small (25.28%) and Desi small (22.48%) against the lowest in Aseel Sindh (6.67%), Dhakki (7.18%) and Zaidy (8.67%). These results are in line with the findings of Ramadan (18). The data concerning to flesh weight also varied significantly among date varieties. Maximum mean value of flesh weight was recorded in Dhakki (12.90g) followed by Aseel Sindh (12.74g) and Choharay (10.91g), while minimum flesh weight was observed in Desi simple (2.00g), Desi red small (3.49g) and Desi small (3.57g) (Table 2). However, maximum mean value of flesh weight percentage was recorded in Aseel Sindh (93.33%) followed by Dhakki (92.82%) and Zaidy (91.30%), against minimum in Desi simple (65.81%) followed by Desi red small (74.72%) and Desi small (77.52%). Ramadan (18) also reported similar results. The data further revealed significant (p ≤ 0.05) differences with respect to fruit diameter and length (Table 2). Dhakki topped in fruit diameter (4.55 cm) with fruit length of 2.22 cm. Aseel Sindh stood second in diameter (3.80 cm) while excelled in fruit length (2.40 cm) against minimum from Desi simple (2.08 cm diameter and 1.30 cm fruit length). Ismail et al. (14) found that length and diameter ranged from 2.85 to 3.66cm, and 2.05 to 2.36cm respectively in five date varieties. Significant (p ≤ 0.05) variations in fruit volume and fruit density also existed among different varieties. Mean value of fruit volume ranged from 3.09cm3 (Desi simple) to 11.94cm3 (Dhakki). Dora basrarwal (11.60cm3) and Aseel Sindh (11.39cm3) stood second and third, respectively. Fruit density in different date varieties ranged from 0.92g/cm3 (Karblain) to 1.25g/cm3 (Shungust). Choharay (1.24g/cm3) and Desi basray (1.23g/cm3) stood at par

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with Shungust. These results agree to those of Ismail et al. (14) who reported 6.94mL to 9.16mL fruit volume and 1.09g/mL to 1.15g/mL density. The data (Table 2) regarding edible/non-edible ratio showed the highest mean value of edible/non-edible ratio in Aseel Sindh (14.50) followed by Dhakki (13.02) and Zaidy (10.82), against the lowest in Desi simple (1.94), Desi red small (3.01) and Desi small (3.51). Ramadan (18) also found similar results.

With regards to water activity also the data (Table 2) reflected significant (p≤0.05) differences among varieties. Maximum water activity was found in Desi basray (0.482) followed by Desi simple (0.479) and Desi red small (0.478). Minimum mean value of water activity was observed in Karblain (0.323) followed by Zaidy (0.333) and Dora (0.346). Fruit colour also differed significantly among different varieties. Maximum mean value of fruit colour was recorded in Desi red small (Table 2) and Desi small (149.10CTn each) followed by Dora (130.80CTn) and Desi green (130.20CTn) (Table 2). Minimum mean values of fruit colour was observed in Choharay (77.40CTn) followed by Aseel Sindh (83.10CTn) and Khopra (95.50CTn). The data (Table 2) further showed significant (p≤0.05) differences in texture force among different date varieties. Maximum texture force was assessed during needle penetration from the peak of graph (Fig.1) which was found in Dora (59.64g) followed by Dhakki (50.94g) and Karblain (42.48g). The lowest mean value of peak force was recorded in Desi simple (14.58g) followed by Desi basray (15.05g) and Desi basraywal (17.17g).

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Fig. 1. Puncture test of date fruit

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Difference in physical properties of date varieties might be attributed to several factors like amount and type of fertilizers, soil and climate and irrigation. Basha and Abo-Hassan (9) explained that soil fertilization affected the weight, length, diameter and volume of Khudravi date fruits. Hussein and Hussein (13) reported that soil fertilization and irrigation contributed to physical properties of date fruits like fruit weight, length, diameter and volume. Proper application of these two factors increased the weight, length and diameter of date fruits. Variation can also be attributed to other environmental factors i.e. daily temperature and length of day and post harvest treatments such as drying. Total phenolic content The results (Fig. 2) revealed significant differences with respect to phenolic content among date varieties. The highest mean value of total phenolic content was recorded in Dhakki (296.67mg) followed by Aseel (283.33mg) and Hillavi (275.67mg). The lowest mean value for this parameter was observed in Desi red small (140.67mg) followed by Desi black (148.0mg) and Shungust (163.33mg). These results agree to those of Al-Farsi et al. (1) who reported the phenolic content of 172-246mg GAE/100g fresh weight in three date varieties grown in Oman. They explained that differences in phenolic content were due to variety, maturity stage, growing conditions and environmental conditions.

Fig. 2. Means of total phenolic content in date varieties

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CONCLUSION The study concludes that Dhakki, Aseel Sindh and Hillavi may be considered suitable for table purpose because of their good physical characteristics like large fruit size, higher fruit weight, flesh weight, edible/non-edible ratio, firm texture and nutritional properties. Other date varieties like Karblain, Zaidy and Dora are suitable for processing due to low moisture content and higher sugar content.

ACKNOWLEDGEMENT The authors acknowledge the generous financial support of Higher Education Commission of Pakistan for conducting this research.

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