J Sci Food Agric 1998, 76, 427È434 Eþects of Type of Packaging Materials on Physicochemical, Microbiological and Sensory Characteristics of Durian Fruit Leather During Storage J Irwandi, Y B Che Man,* S Yusof, S Jinap and H Sugisawa Faculty of Food Science and Biotechnology, Universiti Pertanian Malaysia, 43400 UPM Serdang Selangor DE, Malaysia (Received 9 September 1996 ; revised version received 1 April 1997 ; accepted 9 July 1997) Abstract : A study on storage stability of durian leather was carried out at room temperature using four types of packaging materialsÈlaminated aluminium foil (LAF), high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene (PP) ÐlmsÈfor 12 weeks. Analyses on physicochemical, microbiological and sensory characteristics were conducted at weeks 0, 2, 4, 8 and 12. Analyses for sugar, fat and caloric contents were conducted at the beginning and the end of storage period. Moisture contents and water activity (A ) Ñuctuated w browning during storage but tended to decrease after week 8. Non-enzymatic increased signiÐcantly (P \ 0É05) for all samples in packaging materials used ; the highest increases were observed in LDPE-packed leather. The increases were related to the changes in colour of samples during storage. The longer storage time, the higher L and b values and the lower a value. The pH, although it Ñuctuated in the Ðrst weeks, slightly increased at the end of the storage period, while the hardness for each sample gradually increased during the storage. Microbial analyses showed that total mesophilic bacteria (TMB) and total moulds and yeast (TMY) counts were low, where after 12-week storage TMB and TMY were less than 60 and 140 cfu g~1, respectively. Organoleptically, for all attributes evaluated, all samples were acceptable by panelists during the 12-week storage period. ( 1998 SCI. J Sci Food Agric 76, 427È434 (1998) Key words : Durio zibethinus Murr ; clone D24 ; packaging materials ; organoleptic evaluation INTRODUCTION leather, as an alternative to diversify the uses of durian, has been reported by Irwandi and Che Man (1996). Like other fruit leathers, durian leather was prepared by drying the aril after mixing with other ingredients into leathery sheets. Che Man et al (1997) reported that the additions of glucose syrup solid, sucrose, hydrogenated palm oil and soy-lecithin into durian aril when mixing resulted in an acceptable durian leather. Besides, both oven and cabinet dryers were able to be used in the preparation of the product. Durian leather is an intermediate moisture food (IMF), for which the market is presently growing (Guilbert 1987). Brockmann (1973) stated that the Durian (Durio zibethinus Murr), the most famous of the popular seasonal fruit of South-East Asia, is usually consumed fresh. The aril of the fruit can also be frozen or processed into paste, processed into durian powder or added into other products such as ice cream, cakes and confectionary (Nantachai 1994). Fruit leather, a product prepared by dehydration of fruit puree, is an established product, particularly in the North-American market (Raab and Oehler 1976). Development of durian * To whom correspondence should be addressed. 427 ( 1998 SCI. J Sci Food Agric 0022È5142/98/$17.50. Printed in Great Britain J Irwandi et al 428 recent commercial success of IMF has stimulated interest in this area and in the development of new intermediate moisture product for human consumption. The intermediate moisture products o†er the potential advantage that can be eaten without preparation. They can be consumed directly as fruit snacks or combination with nuts and breakfast cereal. They can also be incorporated in various fabricated foods such as biscuits, cookies and ice creams. Hence, for commercial purposes, the use of suitable packaging materials of durian leather is very important, particularly to prolong the shelf-life of the product. Brockmann (1973) stressed that there are three main parameters normally related to stability of an IMF : water activity, microbiological stability and physicochemical characteristics. The present study was carried out to determine the e†ects of the type of packaging materials used and time of storage on quality of durian leather, including physicochemical characteristics, microbial stability and sensory properties. MATERIALS AND METHODS Materials Durian fruits from Clone D24 were obtained from the Universiti Pertanian Malaysia farm. Glucose syrup solid (GSS) (DE 12È15) and hydrogenated palm oil (HPO) were kindly donated by Stamford Industry, Petaling Jaya, and Palm Oil Research Institute of Malaysia (PORIM), respectively. Sucrose, soy-lecithin (SL), egg yellow colour (Bush Boake Allen) and analytical grade reagents were obtained from local suppliers in Sri Serdang, Selangor DE. All packaging materials usedÈ laminated aluminimum foil (LAF), high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP)Èwere supplied by Malaysian Packaging Sdn Bhd, Selangor. The thickness of each packaging material was 0É10, 0É08, 0É05 and 0É10 mm for LAF, HDPE, LDPE and PP, respectively. enclosed water-bath container at 85È100¡C for 5 min and blended. During blending, 10% GSS, 5% sucrose, 2É67% HPO, 0É45% SL, 30% water and 100 mg kg~1 egg yellow colour were added. Sorbic acid 200 mg kg~1 were also added as preservative. The mixture was then formed into sheets of 1É2 mm thick and dried in both oven and cabinet dryers. For the oven, drying was done at 50¡C for 12É6 h ; for the cabinet, drying was done at 52É5¡C for 10 h. The leathers were then packed and stored at ambient temperature (c 27¡C) for further analyses. Physicochemical analyses Moisture and fat contents were determined according to AOAC (1984) methods. Water activity (A ) was meaw sured using chemical desiccation method described by Rockland (1960). Non-enzymatic browning was determined using spectrophotometry method (Askar and Treptow 1993). A 10-g sample was extracted with 100 ml 60% ethanol for 12 h and centrifugated at 1260 ] g for 5 min. The absorbance of the extract was then measured with a spectrophotometer at 420 nm with 60% ethanol as a blank. Total sugar was determined according to Hunt et al (1977). A HPLC (Waters 410 di†erential refractometer) was used with sucrose, fructose, glucose and maltose as standards. pH was measured using a pH meter (Corning 220) according to Askar and Treptow (1993), while the caloric content was determined using an oxygen bomb calorimeter (Anon 1960). The colour was determined using a Hunter lab colorimeter (Model D25-2). A yellow tile (L \ 77É5, a \ [ 3É5, b \ 23) was used as a reference standard. The texture was measured with Instron Universal Testing Machine (model 1140). Chart and head speeds were kept at 100 mm per min. The values were recorded as the force (in kgf) required to penetrate a 1É2 mm thick sample. The diameter of hole was 8 mm. Analyses for physicochemical changes during storage were carried out in triplicates. Experimental design Durian leather was prepared by using an oven and a cabinet dryer. The durian leathers were then packed in the four di†erent packaging materials. Storage study was conducted for 12 weeks and all analyses were carried out at weeks 0, 2, 4, 8 and 12, except for fat, sugar and caloric contents, which were analysed only at weeks 0 and 12. Sample preparation Durian leather was prepared according to Irwandi and Che Man (1996). Durian aril was blanched in an Microbiological tests Total mesophilic bacteria (TMB) and total mould and yeast (TMY) counts of fresh and stored durian leather were conducted according to Anon (1982). A 10-g sample was added with 90 ml sterile peptone water and blended for 1 min. Aliquots were further diluted to obtain 10~1È10~3 for both TMB and TMY. From each dilution, 1É0 ml was transferred aseptically to Petri dishes, poured with plate count agar (PCA) for TMB, and acidiÐed potato dextrose agar (PDA) for TMY, and incubated for 2È5 days at 37 and 30¡C for TMB and TMY, respectively. Analyses were in triplicates. E†ect of type of packaging materials on durian leather Organoleptic evaluation Sensory analyses for taste, texture, appearance, aroma and overall acceptability were carried out using a 7-point hedonic scales (1 \ dislike extremely, 7 \ like extremely) (Larmond 1977). All organoleptic attributes were evaluated by 20 semi-trained panelists selected from students of the Faculty of Food Science and Biotechnology, Universiti Pertanian Malaysia. All data were assessed by analysis of variance (ANOVA) and least signiÐcant di†erence (LSD) test (Steel and Torrie 1980). RESULTS AND DISCUSSION Moisture content and water activity Moisture content of both oven-dried and cabinet-dried durian leathers Ñuctuated during storage, ranging from 13È17% (Table 1). This is due to di†erences in the moisture vapour permeability of the packaging Ðlms. However, except for cabinet-dried leathers packed in LAF, the moisture content of samples decreased signiÐcantly after week 4. The highest decrease was exhibited by samples packed in LDPE. This was closely related to the characteristics of the packaging materials as shown by Che Man et al (1995). They reported that LDPE had higher water vapour permeability (17É6 g m~1 d~1 at 38¡C, 90% RH), compared with PP (3É38) and HDPE (7É88). The water vapour permeability for LAF is less than 0É5 (Minakuchi and Nakamura 1990). Early work on the stability of dried fruit also showed the e†ects of tropical conditions on prunes, apricots, peaches and pears. Nichols and Reed (1931) found that deterioration at 25¡C took place twice as fast as at 0¡C. They also found that drying to 10% moisture improved the stability of apples, did not a†ect the stability of apricots, but made the pears less stable. They showed further that quality of dried fruit was adversely a†ected by increased time and temperature of storage and by higher moisture content. The importance of moisture content on stability of dried fruit product was also reported by Schwarz (1943), who stressed that moisture and equilibrium relative humidity of dried fruits were very important in designing packages and selecting storage conditions. The initial moisture ranging from 15 to 16% in our present study was suitable for storage purpose of durian leather packed in di†erent packaging materials at ambient temperature. Che Man and TauÐk (1995) reported that jackfruit leather which contained 11È17% moisture and packaged in polyethylene was still acceptable after 2 months storage, while Rao and Roy (1980) reported that the ideal moisture to have storage stability of mango leather was found to be 15% or a little more with a relative humidity between 63 and 70%. 429 However, lowering moisture contents to 10% or below as suggested by Nichols and Reed (1931) might be applied to improve the storage stability of dried fruit product, but in the case of fruit leather it could greatly inÑuence the product texture. The changes in A of durian leather was relatively w similar to the moisture changes (Table 1). There was a clear relationship between moisture content and A : the w higher the moisture content the higher the A . Similar w observations were made on kiwifruit leather by Lodge (1981) and jackfruit leather by Che Man and TauÐk (1995). The A changes were observed as early as the w fourth week of storage. During storage, for leathers packed in LAF, HDPE and PP, the range of A Ñuctuw ated from 0É57 to 0É63, with LAF and PP having a lower Ñuctuation. However, for LDPE-packed leathers, after achieving a maximum value in the fourth week, the A drastically decreased until week 12, where the A w w were even less than 0É55. Table 1 also shows that both the type of packaging materials and storage time signiÐcantly (P \ 0É05) a†ected the A values of the samples. w The low A (0É5È0É65) of the durian leather product w helped to prolong their shelf-life, as most of microbial activities occurs at A greater than 0É7 (Labuza et al w 1970 ; Troller 1980). Che Man and Sanny (1996), who conducted study on storage stability of jackfruit leather, reported that A of 0É63 was well below the minimum w value needed to support microbiol growth. They also found that, during storage, LAF has the lowest decrease in A , and they recommended that this material could w maintain the desired textural characteristic of fruit leather. Non-enzymatic browning and colour Table 1 shows that, for both dryers used, the type of packaging materials and storage time had signiÐcant (P \ 0É05) e†ects on non-enzymatic browning of durian leather, with LDPE showing the highest degree of browning. During storage, the degree of browning shown by samples packed in LDPE was signiÐcantly di†erent (P \ 0É05) from the samples in other packaging materials. Results also indicated that the non-enzymatic browning of LAF, HDPE and PP samples were not statistically di†erent until week 8. Table 1 also shows that, during storage, the degree of browning gradually increased for both dryers used, where absorbances (at j \ 420 nm) of all samples increased from 0É2 at week 0 to 0É3È0É63 at week 12. The highest increase was exhibited by LDPE-packed samples (absorbance \ 0É6È 0É62 after 12 weeks), compared with samples packed in LAF, HDPE and PP (absorbance \ 0É35È0É45 after 12 weeks). Browning could also be due to oxygen e†ects on other compounds in the fruit. Moreover, lightness (L ), redness (a) and yellowness (b) values of the leathers were also signiÐcantly (P \ 0É05) 430 TABLE 1 Physicochemical and microbiological changes of durian leather in di†erent packaging materials during storagea T ype of packaging Moisture (%) Water activity Non-enzymatic browning (absorbance at 420 nm) Texture (kgf ) pH Lightness Redness Yellowness Total mesophilic bacteria (cfu/g) Total moulds and yeast (cfu/g) Cabinet-dried leather, week 0 2 4 8 12 0 2 4 8 12 15É82aA 15É82aA 15É82aA 15É82aA 0É597bA 0É597aA 0É597bcA 0É597aA 0É204eA 0É204eA 0É204eA 0É204eA 0É347bA 0É347dA 0É347dA 0É347dA 6É87abA 6É87abA 6É87bA 6É87aA 66É01aA 66É01aA 66É01aA 66É01aA [0É98aA [0É98dA [0É98dA [0É98dA 35É64aA 35É64aA 35É64aA 35É64aA 16É57dA 16É57eA 16É57eA 16É57eA 16É7eA 16É7dA 16É7dA 16É7dA 15É48abB 16É85aA 15É77aA 17É17aB 0É593bcA 0É597aA 0É607abA 0É597aA 0É240dc 0É259dB 0É274dA 0É246dBc 0É390abB 0É447cAB 0É493cA 0É470cAB 6É60cA 6É67bA 6É60cA 6É68aA 64É55aA 62É89bB 62É88bB 62É81bB [0É83cC 1É36cB 3É34cA 1É22cB 35É78aA 34É43aA 34É47aA 34É79aA 20É90cC 28É50dA 27É13dA 25É37dB 34É7dB 51É7cA 51É3cA 51É7cA 15É35abA 16É02aA 14É96abA 15É76bA 0É620aA 0É607aAB 0É617aA 0É593aB 0É272cB 0É288cB 0É348cA 0É275cB 0É400abB 0É513bcA 0É570bcA 0É533bcA 6É63bcB 6É63bB 6É97bA 7É07aA 61É71bA 61É85bcA 61É66bA 61É56bA 1É17bC 3É13bB 5É10bA 3É59bB 33É33aA 32É31bAB 30É72bB 32É65bAB 27É03bC 36É50cA 31É00cB 31É83cB 51É7bB 71É7bA 76É7bA 68É3bA 14É57abB 15É99aA 14É39bB 15É33bAB 0É597bA 0É580bA 0É580cA 0É587aA 0É354bB 0É370bB 0É428bA 0É377bB 0É460aB 0É583abA 0É647bA 0É600abA 7É07aA 6É83abA 7É00bA 7É10aA 59É61cA 59É85cA 57É14cA 59É11cA 3É49aC 4É13abBC 4É66bA 4É60abB 30É53bA 29É17cA 24É76cB 28É26cA 30É43aB 40É43bA 40É17bA 40É67bA 62É00aB 110É0aA 108É3aA 100É0aA 14É36bA 13É66bA 12É17cB 13É88cA 0É573cA 0É573bA 0É523dB 0É576aA 0É376aC 0É407aB 0É618aA 0É418aB 0É483aC 0É660aB 0É750aA 0É640aB 7É07aB 7É17aAB 7É23aA 7É17aAB 56É41dA 53É82dB 50É75dC 53É66dB 4É62aC 5É78aB 8É82aA 5É93aB 29É16bA 25É30dB 23É37cC 25É44dB 28É60abC 47É67aB 49É83aA 48É67aAB 41É7cC 105É0aB 116É0aA 101É0aB 15É29aA 15É29abA 15É29bA 15É29abA 0É603aA 0É603aA 0É603bA 0É603aA 0É192eA 0É192eA 0É192eA 0É192eA 0É387cA 0É387dA 0É387eA 0É387eA 7É00aA 7É00aA 7É00abA 7É00abA 66É66aA 66É66aA 66É66aA 66É66aA [1É12dA [1É12dA [1É12eA [1É12dA 35É15aA 35É15aA 35É15aA 35É15aA 19É27dA 19É27eA 19É27eA 19É27eA 19É3dA 19É3eA 19É3eA 19É3dA 14É90aB 16É22aA 17É07aA 16É08aA 0É613aA 0É613aA 0É603bA 0É603aA 0É218dC 0É235dB 0É251dA 0É243dAB 0É450bB 0É463cAB 0É487dA 0É470dAB 7É07aB 6É77bAB 6É80bA 6É87bAB 63É34bA 64É13bA 62É19bB 63É73bA 0É12cdB 1É95cA 2É02dA 1É83cA 34É97aA 34É96aA 33É62bB 34É89aA 24É23cB 26É43dA 27É50dA 26É33dA 35É7cB 40É7dB 56É7dA 41É7cB 15É37aA 15É54abA 15É81bA 15É30abA 0É617aAB 0É600aC 0É623aA 0É607aBC 0É255cC 0É282cC 0É379cA 0É308cB 0É417cC 0É587bA 0É600cA 0É517cB 6É93aA 6É83abA 6É93abA 6É83bA 62É84bA 62É86bA 61É34bB 61É88bAB 1É42bcB 3É10bA 3É60cA 2É93cA 33É47aA 31É23bBC 30É07cC 31É85bAB 28É83bB 28É93cB 31É23cA 30É83cA 56É7bC 63É3cBc 83É7cA 70É0bB 14É85aA 14É60bcA 12É05cA 14É96bcA 0É600abA 0É573bB 0É580cB 0É590abAB 0É303bB 0É361bB 0É433bA 0É364bB 0É500aC 0É607abB 0É683bA 0É623cB 7É13aA 6É93abB 7É00abB 6É90abB 60É24cA 59É33cAB 55É23cC 58É09cB 2É66bB 3É56bAB 6É03bA 4É25bB 30É53bA 29É17bAB 24É76dC 28É26cB 30É83aB 37É87bA 40É37bA 38É90bA 72É3aC 106É3aB 108É3bA 101É7aAB 15É27aA 13É75cB 12É05cC 13É96cB 0É583bA 0É577bA 0É517dB 0É580bA 0É345aB 0É414aB 0É603aA 0É419aB 0É513aC 0É650aB 0É817aA 0É717aB 7É03aA 7É03aA 7É17aA 7É10aA 56É51dA 53É71dB 50É41dC 53É41dB 4É53aC 5É59aB 8É33aA 5É76aB 28É32cA 24É96cB 21É76eC 25É47dB 27É87bC 48É90aA 50É53aA 43É83aB 49É0bC 93É3bB 124É3aA 98É3aB a Mean of three replicates. AhC Means within a column with di†erent letters are signiÐcantly di†erent (P \ 0É05). ahe Means within a row with di†erent letters for each dryer are signiÐcantly di†erent (P \ 0É05). J Irwandi et al LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP LAF HDPE LDPE PP Oven-dried leather, week E†ect of type of packaging materials on durian leather 431 TABLE 2 Mean values (^SD) for sugar, fat and caloric content of fresh and 12-week stored durian letters Oven Sugar (%) Fat (%) Caloric (kcal per 100 g) Cabinet Sugar (%) Fat (%) Caloric (kcal pers 100 g) W eek L AF HDPE L DPE PP 0 12 0 12 0 12 45É5 ^ 1É6aA 42É2 ^ 1É3aA 4É1 ^ 0É3aA 3É6 ^ 0É1bA 638 ^ 13aA 499 ^ 7bAB 45É5 ^ 1É6aA 42É1 ^ 2É3aA 4É1 ^ 0É3aA 3É5 ^ 0É1bAB 638 ^ 13aA 477 ^ 7bB 45É5 ^ 1É6aA 41É4 ^ 0É9bA 4É1 ^ 0É3aA 3É4 ^ 0É2bB 638 ^ 13aA 492 ^ 5bAB 45É5 ^ 1É6aA 41É9 ^ 1É5bA 4É1 ^ 0É3aA 3É5 ^ 0É1bAB 638 ^ 13aA 466 ^ 5bB 0 12 0 12 0 12 43É7 ^ 1É2aA 42É1 ^ 1É5aA 4É2 ^ 0É2aA 3É7 ^ 0É1bA 643 ^ 17aA 492 ^ 5bA 43É7 ^ 1É2aA 41É6 ^ 1É4aA 4É2 ^ 0É2aA 3É5 ^ 0É1bAB 643 ^ 17aA 469 ^ 15bB 43É7 ^ 1É2aA 41É0 ^ 0É6bA 4É2 ^ 0É2aA 3É3 ^ 0É2bB 643 ^ 17aA 475 ^ 12bAB 43É7 ^ 1É2aA 41É1 ^ 1É1aA 4É2 ^ 0É2aA 3É5 ^ 0É1bAB 643 ^ 17aA 488 ^ 7bAB ahb Means with a column with di†erent letters are signiÐcantly di†erent (P \ 0É05). AhB Means within a row with di†erent letters are signiÐcantly di†erent (P \ 0É05). a†ected by the type of packaging materials and time of storage (Table 1). L values decreased signiÐcantly (P \ 0É05) during storage, and the decrease was greatest for the leathers packed in LDPE, followed by PP, HDPE and LAF. A similar decrease was also seen in the b values. However, unlike L values, the b values for leathers packed in HDPE and PP were not signiÐcantly di†erent. Inversely, the a values increased signiÐcantly (P \ 0É05) for leathers packed in all materials used. It could be concluded that, as the L and b values decreased, the a value increased. The means of a values at week 0 for the two types of dryer used were negative (Table 1), indicating that the samples were more green. The changes in L , a and b values during storage were related to non-enzymatic browning reaction, as mentioned above. E†ect of processing and storage on colour quality of fruit product has been reported by Askar and Treptow (1993). According to them, heat processing and subsequent storage of fruit products is often accompanied by an unattractive discolouration, perhaps due to nonenzymatic browning or oxygen e†ects on other compounds in the fruit. Three factorsÈprocessing condition, storage time and temperatureÈinÑuence the colour of the product ; non-enzymatic browning is considered one of the major causes of quality loss of fruit products. Discolouration of fruit leather during processing and storage were also reported by almost every researcher who conducted studies on fruit leather (Chan and Cavaletto 1978 ; Rao and Roy 1980 ; Che Man and Sanny 1996 ; Che Man and TauÐk 1996 ; Irwandi and Che Man 1996). In the case of durian, Suyitno (1984) also reported the similar phenomenon in durian powder product. Texture Both the type of packaging materials and time of storage had signiÐcant (P \ 0É05) e†ects on the texture (Table 1). Generally, the hardness increased during storage, as shown by the increase in texture unit (kgf). However, for both dryers used, LAF seemed to be the best material for maintaining the desired texture of durian leather, while samples packed in LDPE had the greatest increase in hardness until week 8. For the ovendried product, there was no signiÐcant di†erence between LDPE, PP and HDPE. Meanwhile, for the cabinet-dried product, HDPE and PP were not signiÐcantly di†erent, except for samples at week 4. The results showed that the textural characteristic of durian leather was closely related to moisture content of the sample and water vapour permeability of the packaging material. These changes in water content resulted in signiÐcant changes in the texture, as shown by the measured shear forces. pH The acidity level, indicated by pH, of durian leathers tended to Ñuctuate during storage (Table 1). In the Ðrst 2 weeks of storage, except for the cabinet-dried leather packed in LAF, the pH values of samples decreased ; however, the pH then increased gradually until week 12. At the end of the storage time, the pH values ranged from 7 to 7É25, with LDPE having the highest pH. The mean pH value during storage for oven-dried leathers packed in PP was 7É01, while the leathers in LDPE, HDPE and LAF were 6É93, 6É84 and 6É85, respectively. However, for cabinet-dried leathers, the highest mean pH value during storage was exhibited by the leathers J Irwandi et al 432 packed in LDPE (6É97), followed by PP (6É94), HDPE (6É91) and LAF (6É91). Che Man and Sanny (1996) also showed the Ñuctuation of pH values of jackfruit leather during 3 months storage. Similar observations, where the pH tended to increase at the end of the storage time, was also reported (Che Man and Sanny 1996). Sugar, fat and caloric contents Table 2 shows mean values for sugar, fat and caloric contents for oven-dried and cabinet-dried durian leathers packed in LAF, HDPE, LDPE and PP, analysed at weeks 0 and 12. There was no signiÐcant e†ect of the type of packaging material for each time of storage on the sugar content of durian leather. The sugar contents of all samples seemed to decrease during 12 weeks storage, due to the dilution e†ect as the moisture increased. However, for oven-dried leathers, only samples packed in LDPE and PP had a signiÐcant (P \ 0É05) decrease ; for cabinet-dried leathers, a signiÐcant (P \ 0É05) decrease was only exhibited by samples in LDPE. The results also showed that the decrease was exhibited by all four types of sugar found in durian of D24 : sucrose, fructose, glucose and maltose. The decrease was also closely related to the browning and the colour changes discussed before. The similar trend of total sugars was also observed by Rao and Roy (1980). The 12 weeks of storage also had a signiÐcant (P \ 0É05) e†ect on fat and caloric content for samples in all packaging materials used, those dried by both oven and cabinet. Samples packed in LDPE had the greatest decrease (P \ 0É05) in fat content during storage, but no signiÐcant di†erence among the other materials. In term of caloric content, LAF was seen to have the lowest decrease during storage. The fresh durian leather in this study was 638 kcal per 100 g for oven-dried leathers and 643 kcal per 100 g for cabinetdried leathers. At the end of the storage time, the caloric contents of the samples dried by oven were 499, 477, 492 and 466 for LAF, HDPE, LDPE and PP, respectively ; for samples dried by cabinet, the values were 492, 469, 475 and 488, respectively. Although there was a signiÐcant decrease of durian leather during 12 weeks of storage, the “statusÏ of durian leather as a rich-caloric snack food (Irwandi and Che Man 1996) was still maintained, even at the end of the storage time. As a comparison, the caloric content of fresh jackfruit leather as reported by the Che Man and TauÐk (1995) was only 348 kcal per 100 g. Microbial analyses Results from Table 1 indicate that the type of packaging materials and time of storage both signiÐcantly (P \ 0É05) a†ected the microbial growth during storage. From the results, LAF seemed to be the Ðnest material to inhibit the growth of the mesophilic bacteria, mould and yeast. Table 1 also shows that, apart from LAF, TMB gradually increased from less than 20 cfu g~1 at week 0 to 40È50 cfu g~1 at week 12, with the highest TMB exhibited by leathers packed in LDPE, followed by PP and HDPE for oven-dried leather and HDPE and PP for cabinet-dried leather. The TMB for LAF showed a di†erent pattern, where the highest TMB was reached at week 8, and decreased thereafter. The turning points at week 8 were also showed by TMY for both oven-dried and cabinet-dried leathers. It seamed that only LDPE-packed leathers had increasing TMY up to 12 weeks of storage. This indicated that, for durian leather, week 8 could be considered as a maximum point for moulds and yeast growth. The decrease in TMY counts after week 8 could be caused by the decrease in the nutrients supporting the microbial growth or unsuitable environment due to production of some toxic compounds by the microbe itself (Fardiaz 1989). In the case of TMB counts, during 12 weeks of storage, the maximum points could be detected only for samples packed in LAF, while samples packed in HDPE, LDPE and PP may be reached their optimum points after week 12. Jayaraman (1987) reported that the maximum points for total plate counts (TPC) and total moulds count of stored mango leather was also reached at week 8 ; for banana leather, the highest TPC and yeast counts were achieved after 6 months storage. However, no moulds were found in this study. Overall, both TPC and TMY of samples kept for 12 weeks in all packaging materials were very low (less than 60 cfu g~1 for TPC and 140 cfu g~1 for TMY). This indicated that the durian leathers were resistant to bacteria, mould and yeast growths and microbiologically safe for direct consumption. The low counts of TMB and TMY in this study was closely related to the low A of the samples. According to Christian (1963), w foods with A lower than 0É6 are essentially free from w microbial growth. The low counts was also due to presence of sorbic acid. Moulds are more e†ectively inhibited by mycostatic agents such as sorbic acid (Christian 1963). Sensory characteristics during storage Table 3 shows the sensory characteristics of durian leather during storage. In terms of taste, there was no signiÐcant di†erence for the four types of packaging materials used, but the type of material had signiÐcant (P \ 0É05) e†ects on texture, appearance, aroma and overall acceptability. For both oven-dried and cabinetdried leathers, results also showed that panelists gave the lowest score of texture, appearance, aroma and T ype of packaging Oven-dried leather, week Cabinet-dried leather, week 0 2 4 8 12 0 2 4 8 12 Taste LAF HDPE LDPE PP 5É75aA 5É75aA 5É75aA 5É75aA 5É85aA 5É80aA 5É60abA 5É70abA 5É60abA 5É51aA 5É30abA 5É39abcA 5É29bA 5É25abA 5É18bA 5É22bcA 5É12bA 4É98bA 4É51cA 5É05cA 5É82aA 5É82aA 5É82aA 5É82aA 5É80aA 5É75aA 5É70abA 5É77abA 5É69aA 5É47abA 5É50abA 5É52abA 5É41aA 5É29abA 5É14bA 5É22bA 5É20aA 5É00bA 4É64cA 4É99bA Texture LAF HDPE LDPE PP 5É91aA 5É91aA 5É91aA 5É91aA 5É77aA 5É65abA 5É60abA 5É70abA 5É60aA 5É47abcA 5É18bcA 5É39bcA 5É54aA 5É20bcAB 4É77cB 5É18cAB 5É47aA 4É96cA 3É98dB 4É88cA 6É00aA 6É00aA 6É00aA 6É00aA 5É75aA 5É73aA 5É66aA 5É70abA 5É80aA 5É42abA 5É28aA 5É45abA 5É62aA 5É28bA 4É51bA 5É20abB 5É55aA 5É00bA 4É05bB 4É98bA Appearance LAF HDPE LDPE PP 6É51aA 6É51aA 6É51aA 6É51aA 6É50aA 6É45aA 6É30aA 6É39aA 6É25abA 6É18abA 5É95aA 6É10abA 6É05abA 5É77bA 5É10bB 5É65bAB 5É76bA 5É17cB 4É12cC 5É20cB 6É54aA 6É54aA 6É54aA 6É54aA 6É50abA 6É33abA 6É20abA 6É40abA 6É10abcA 6É10bcA 5É85bA 6É05bcA 6É02bcA 5É62cdAB 5É21cB 5É70cdAB 5É92cA 5É25dB 4É21dC 5É31dB Aroma LAF HDPE LDPE PP 5É60aA 5É60aA 5É60aA 5É60aA 5É64aA 5É50aA 5É55abA 5É55aA 5É58aA 5É25aA 5É10abcA 5É35abA 5É45aA 5É00abAB 4É85bcB 4É90bAB 5É25aA 4É75bA 4É55cA 4É70bA 6É00aA 6É00aA 6É00aA 6É00aA 5É90aA 5É80aA 5É80abA 5É85abA 5É90aA 5É70aA 5É50bA 5É75abA 5É70aA 5É20bB 5É10cB 5É33bAB 5É50aA 4É95bA 4É75dA 4É80bA Overall acceptability LAF HDPE LDPE PP 6É05aA 6É05aA 6É05aA 6É05aA 5É97abA 5É83abA 5É27abB 5É77abAB 5É90abA 5É48bcAB 5É05abcB 5É60abAB 5É48bcA 5É22cdA 4É65bcB 5É31bcA 5É25cA 4É90dA 4É08cB 4É92cA 6É10aA 6É10aA 6É10aA 6É10aA 6É00abA 5É80abA 5É33aB 5É65abAB 5É80abA 5É55abAB 5É02abB 5É60abAB 5É40abA 5É16bB 4É51bcC 5É10bB 5É20bA 5É00bA 4É12cB 4É97bA E†ect of type of packaging materials on durian leather TABLE 3 Sensory characteristics changes of durian leather in di†erent packaging materials during storagea a Mean of 20 panelists. AhC Means within a column with di†erent letters are signiÐcantly di†erent (P \ 0É05). ahd Means within a row with di†erent letters for each dryer are signiÐcantly di†erent (P \ 0É05). 433 J Irwandi et al 434 overall acceptability to LDPE-packed samples and the highest scores to samples packed in LAF. On the other hand, for several attributes, the use of HDPE and PP did not give a signiÐcant e†ect. There was a signiÐcant e†ect (P \ 0É05) of storage time on the sensory qualities of durian leather. However, for almost every attribute evaluated, there was no signiÐcant di†erence for the Ðrst 2 weeks. Only overall acceptability of oven-dried leather had a signiÐcant di†erence after 2 weeks of storage. In fact, for taste and aroma of oven-dried leathers, and taste, texture and overall acceptability of cabinet-dried leathers, no signiÐcant di†erences were observed up to week 4. Besides, the scores of all sensory attributes signiÐcantly (P \ 0É05) decreased, with the highest decrease found for leathers packed in LDPE and the lowest changes for LAF-packed leathers. Overall, all samples were acceptable (score more than 4), even after 12 weeks of storage. CONCLUSIONS Out of four types of packaging materials used, LAF was found to be the best material to maintain the stability of durian leather during storage. During 12 weeks of storage, LAF had the lowest changes in moisture content and A , a lowest decrease in colour quality and w a lowest increase in microbiol counts. Inversely, LDPE had a highest changes in moisture and water activity, a highest decrease in colour quality and a greatest increase in microbial counts. This was closely related to the water vapour characteristics of the packaging materials. However, organoleptically, all four packaging materials were acceptable. 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