A RESEARCH NOTE OBJECTVE COLOR MEASUREMENT OF FRESH DATE FRUTS AND PROCESSED DATE PRODUCTS SUAD AL-HOOTP3 and J.S. SDHU' 'Biotechnology Department Kuwait nstitute for Scientific Research P.O. Box 24885 13109 Safat, Kuwait City, Kuwait AND H. QABAZARD 'Palm Agro-Production Company P.O. Box 976 13020-Safat Kuwait City, Kuwait Accepted for Publication April 14, 1996 ABSTRACT Because of significant international trade in date fruits, the need for objective color measurement for maintaining strict quality standards has become obvious. The results on color measurement of specimens of fresh date fruits at four stages of maturity and some processed date products in tern of CE L*a*b* color coordinate values and hue angle (v) arepresented. The L*, a*, b* and q values were found to indicate the color of date fruits and processed date products objectively. Measurements utilizing a Macbeth Color Checker spectrophotometer may, therefore, be extremely useful in quantifying the color of date fruits for objective color comparison between different date cultivars and for quality control of processed date products in the international trade. 3T0 whom correspondence should be addressed. Journal of Food Quality 20 (1997) 257-266. All Rights Reserved. "Copyright 997 by Food & Nutrition Press, nc., Trumbull, Connecticut. 257
258 S. AL-HOOT, J.S. SDHU and H. QABAZARD NTRODUCTON For centuries, the date (Phoenix dactylifera L.) has been an important crop in the desert regions of Middle Eastern countries for the survival of many ancient nomads (Mohammed et al. 1983). At present, approximately 2000 or more different date-palm cultivars are known to exist all over the world, but only a few important ones have been evaluated for their performance and fruit quality. Rygg (1975) has given a detailed description of the date growing regions of the world, varieties and general culturing practices. The color of foods is due to the presence of various naturally occurring or added pigments or development during processing of complex chemical or biochemical (enzymatic or nonenzymatic) changes that take place in the food systems (Archana et al. 1995). Color and appearance constitute the first attribute considered by the consumer when selecting a food product for consumption. As the natural food pigments have poor stability, a judicious selection of processing conditions has been suggested for their maximum retention (Clydesdale 1984). The change in color during the preparation of food has been shown to be a useful index of the degree of cooking or processing the food product has undergone (Birch et al. 1977). Due to the limitations of sensory methods of color measurement, instrumental methods are gaining importance (Mazza and Oomah 1994). No information is available in the literature on the use of instrumental methods for measuring the color of date fruits or processed date products. The present study has been undertaken to measure the color of five cultivars of date fruits at different stages of maturity as well as those of some processed date products. Sample Collection MATERALS AND METHODS Date fruit samples from five cultivars, viz., Gash Gaafar, Gash Habash, Shahla, Bushibal and Lulu, were collected personally by a colleague visiting the United Arab Emirates and in cooperation with the Palm Agro-Production Company (Kuwait). The fruits were collected at predetermined time intervals (dependent upon the pollination dates) covering different stages of fruit maturity throughout the 1994 date-palm fruiting season. The pollination date for the Gash Gaafar, Gash Habash, Shahla, Bushibal and Lulu varieties were January 15, February 10, February 10, January 10 and January 30, 1994, respectively. The fruits were taken from trees that had been randomly selected and marked for the study. Samples were collected at four stages of fruit maturity, i.e., kimri,
COLOR MEASUREMENT OF DATE PRODUCTS 259 khalal, rutab, and tamr (Hussein 1970), from all five cultivars, except the rutab stage from the Shahla cultivar, for which only a small quantity was obtained. The time of picking fruits for these cultivars was 12, 16, 18 and 20 weeks after the date of pollination for kimri, khalal, rutab and tamr stages, respectively. At kimri stage the fruits from these cultivars have a hard texture, green color and can be used for making pickles and chutney. During the khalal stage, fruit from each cultivar develops its typical yellow, red or yellow-scarlet color, but retains a firm texture and can be used for jam, butter, dates-in-syrup or for eating as fresh dates. Rutab stage is characterized by softening of the half of the fruit with the development of dark color and increased sweetness. Date fruits at the rutab stage can be used for making jam, butter, date bars, date paste or eaten as fresh fruit. During the tamr stage, the whole of the fruit becomes wrinkled, soft in texture, relatively drier, dark gray-black in color and develops maximum sweetness (Al-Hooti et al. 1995). At the tamr stage, dates can be further dried in the sun for prolonged shelf life and storage. Sample Preparation All of the freshly received fruit samples were washed thoroughly in running tap water and subsequently air-dried. After removal of the calyxes, the fresh date fruits were used for the color measurement. The preparation of various date products evaluated for objective color measurements in this study have been described by Al-Hooti et al. (1996a). The pickle-in-oil and chutney are spiced moderately and preserved in mustard oil. Pickle-in-vinegar dates, more or less, resembles cucumber pickles in acidity content and appearance. Although date jam is similar to any standard fruit jam, it has a higher ph (4.6) as well as total soluble solids (75" Brix). n addition to rutab stage date fruit pulp, a relish may be formulated by incorporating carrots, onions, raisins and sliced khalal stage date fruits. For dates-in-syrup, peeled khalal stage date fruit is briefly cooked (3-5 min) in boiling sugar syrup (75" Brix), hot-filled in glass jars and immediately capped. Objective Color Measurement The color of date fruits at different stages of maturity, as well as that of processed date products, was measured with a Macbeth Color Checker (model 545) portable spectrophotometer as CE L*a*b* and hue angle (q) values (Kollmorgon nstruments Corporation 1991). n this coordinate system, the L* value is a measure of lightness ranging from 0 (black) to 100 (white), the a* value ranges from -100 (greenness) to + 100 (redness), and the b* value ranges
260 S. AL-HOOT, J.S. SDHU and H. QABAZARD from -100 (blueness) to +lo0 (yellowness). As the values of a* and b* rise, the color becomes more chromatic or saturated. These values approach zero for neutral colors (white, grey, black). The instrument settings were lluminant D50, Display L*a*b*, Observer 2". The instrument was calibrated with a white primary tile supplied by the manufacturer. Twelve readings were taken on each sample. After eliminating the two most extreme readings, the remaining ten were averaged and recorded along with their standard deviation. RESULTS AND DSCUSSON Visual Color of Date Fruits All the cultivars were green in color at the kimri stage; but by the khalal stage, the cultivars had developed different colors, At the khalal stage, Shahla and Bushibal fruits were red, Gash Gaafar and Lulu fruits were yellow, and Gash Habash fruits were yellow-scarlet. As the date fruits matured further to the next stage, their color and texture changed significantly. All of the date fruits at the rutab stage had developed a dull brown color, starting from the distal end. By the tamr stage, the fruits had turned dark brown-black in color. The yellow color of Gash Gaafar and Lulu fruits is a desirable trait for their suitability for processing into pickles, chutney and dates-in-syrup. At the rutab stage, half of each fruit becomes soft and develops a dark brown color, while at the last stage, tamr, the fruit turns dark brown-black and becomes wrinkled. The red color of Shahla and Bushibal fruits at khalal and rutab stages has been earlier reported to be suitable for processing into jam and date-butter (Al-Hooti ef al. 1996a). The Bushibal and Lulu cultivars at khalal stage of maturity are quite popular and valued for consumption as fresh dates (Al-Hooti et al. 1996b). Objective Color Measurements The CE L*a*b* and hue angle values for fresh date fruits at four stages of development from different cultivars are presented in Table 1. As can be seen from the data in this table, the date fruits at the kimri stage were light green in color with a slight yellowish tinge, which is indicated by the positive b* values. At the kimri stage, fruits from all the cultivars showed lightness values in a narrow range, but at the rutab and tamr stages, the lightness values decreased. However, by the khalal stage, the Bushibal, Gash Habash and Shahla fruits had developed a reddish color (higher positive a* values). Gash Gaafar and Lulu
COLOR MEASUREMENT OF DATE PRODUCTS 26 1 fruits were yellow in color (higher b and h and a values). Comparing b* and a* values of Gash Gaafar and Lulu fruits at khalal stage, the former is more than three times the later in magnitude; it is, therefore, a major contributor to chroma and is responsible for making these cultivars to appear more yellowish in hue than others. The higher a* values indicate its dominant role in chroma of red colored khalal fruits of Bushibal, Gash Habash and Shahla cultivars. At the rutab and tamr stages, the color of the date fruits was darker (lower L* values), and had reached a neutral grey-black (the a* and b* values approached almost zero). TABLE 1. CE L* a* b* AND HUE ANGLE VALUES FOR DATE FRUTS OF VAROUS CULTVARS AT DFFERENT STAGES OF MATURTY Kimri Khalal Rutab Tamr 48.23i2.01 32.22i2.03 10.29il.75 17.47i2.82 48.84k1.19 50.82~1.31 45.74~2.21 49.75i0.65 69.90k2.69 47.47k2.49 64.71.rO.76 38.48k1.66 26.22i1.20 33.86k1.93 41.57i3.67 21.97t2.13 22.86k2.68 23.83i1.48 20.76i1.19 23.05.rO.95 Kimri -8.82iO.39-10.39iO.82-10.10+0.45 Khalal 25.31i1.26 16.88k1.53 36.10i1.51 Rutab 3.71+1.07 8.93+2.29 12.65i1.61 Tamr 2.09.rO.72 3.76i1.30 7.7851.56-10.12*0.32-9.73+0.32 12.79~0.29 26.4713.20 14.67i1.20 10.53i1.64 4.12iG.85 6.3021.38 Kimri 24.43k0.77 26.22k1.20 26.04i1.64 22.43.rl.57 Khalal 9.7720.46 53.42?2.04 25.93k2.20 43.48i0.56 Rutab 9.59i1.49 8.61i2.29 15.08i2.05 24.0822.99 Tamr 0.43iO.25 1.94iO.81 3.69t0.57 2.19k0.53 23.61~1.18 15.45i1.04 11.98i2.79 2.83i0.54
CE a* value Hue (theta) angle FG. 1. CE L* a* b* AND HUE ANGLE (THETA) (MEAN & S.D.) OF PCKLE AND CHUTNEY SAMPLES MADE FROM DATE FRUTS OF DFFERENT CULTVARS AT KJMR STAGE OF MATURTY BB = Bushibal, GG = Gash Gaafar, GH = Gash Habash, L = Lulu, SH = Shahla N a.n CE L' value 40 35 m P0 PV CUTNEY P0 PV CHUTNEY CE b* value i i 80 i GG Gl 1 PV CHUTNEY i P0 PV CHUTNEY
COLOR MEASUREMENT OF DATE PRODUCTS 263 P rl P m w H U 3 0 0 0 0 0 0 U m 3 1 e m
40 35 0, 0 CE L* value i 25 ' 20 l5! 1 10 CE a* value hmmm UB LL bll 5 JAM RELSH U JAM RELSH BUTTER DS CE b* value liue (theta) angle 'll nu 70 i BUTTER DS JAM RELSH BUTTER DS JAM RELSH FG. 3. CE L* a* b* AND HUE ANGLE (THETA) (MEAN f S.D.) OF PROCESSED PRODUCTS MADE FROM DATE FRUTS OF VAROUS CULTVARS AT DFFERENT STAGES OF MATURTY
COLOR MEASUREMENT OF DATE PRODUCTS 265 The a* value being negative, indicates the green color of date fruits at kimri stage of maturity. The positive a* value with lower lightness values in khalal fruits of Bushibal, Gash Habash and Shahla cultivars show these fruits to be of darker red color. Decreased hue angle (h values), lightness (L*), a* and b* values for tamr fruits of all date cultivars reflect the presence of darker grey-black color at this stage of maturity. The objective color measurements made on date fruits using the Macbeth Color Checker spectrophotometer and the data presented here corroborate the visual observations made on these date fruits. CE L*a*b Color Values for Processed Date Products The color of pickles and chutney made from kimri- and khalal-stage fruits was measured objectively using a Macbeth Color Checker in terms of L*, a*, b* and 7 values; the results are shown in Fig. 1 and 2, respectively. The lightness value data shows that the products made from kimri-stage fruits (least mature) were darker in color than those from khalal-stage fruits. The yellow color of the chutney made from khalal-stage fruits was more saturated and chromatic (higher b* and 7 values) than in chutney made from kimri fruits. Pickle samples made from both the kimri as well as khalal stages of maturity also possessed darker yellow color with higher b* and hue angle values (Fig. 2). The lightness values for date jam, relish, and dates-in-syrup (Fig. 3) indicate that these products were much brighter in color than date butter. Date jam from Gash Gaafar and Gash Habash fruits, and date relish from all the cultivars had an attractive reddish color (higher a* values). However, the dates-in-syrup samples retained an attractive yellow color, as shown by their higher b* and 1) values. The evaluation of the data presented in Fig. 1-3 indicates that the Macbeth Color Checker 545 reflectance spectrophotometer is quite useful for objectively measuring the color of processed date products. Measurements made by the Macbeth color checker spectrophotometer would, therefore, be extremely useful in quantifying the color of date fruits for color comparison between different date cultivars for the purpose of processing into value added products or for quality control during international trade. ACKNOWLEDGEMENTS The authors thank the Palm Agro-Production Company, Kuwait, and the Kuwait Foundation for the Advancement of Science for partial funding, the management of the Kuwait nstitute for Scientific Research (KSR) for their continued support of this research work, and Ms. Amani Al-Othman, Division of nformation Systems, KSR, for statistical analysis.
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