Dehydrating Unripe Date Fruits Using Solar Dryer

Dehydrating Unripe Date Fruits Using Solar Dryer Adel Aboel Soaud Horticulture Research Institute, ARC [email protected] Figure 1. ‘half Rutab’ date fruit of the predominant cultivar in Pakistan ‘Aseel’. ABSTRACT Solar dehydration is an old process for food preservation. Purpose to dehydrate the full matured date fruit is to reduce the water content into 25% or less of the fresh weight to preserve the fruit quality after harvesting or during storage. Date fruit contains up to 65% moisture at Khalal stage and decreases into 30-40% by ripening stage (Rutab stage) and less than 20% in the dry varieties by the time of Tamer stage while fruit remains on the tree. Problem appears when the fruit have to be harvested unripe due to inadequate ambient conditions. It could be monsoon rains coincidence during ripening like in Jordan, Palestine, Morocco, Tunisia, USA and Pakistan. Consequently the unripe fruit cured under sun radiation for approximately 6 days exposed to dirt, pest attack or/and sudden rain fall. Otherwise alternative methods including the solar dryers used. There have diferent types of solar tunnels been using in diferent countries but the capacity was limited of 200-400 Kg of unripe fruit approx. per cycle, cost at high level and more efort required. Recently a design of solar tunnel 10 KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION was installed by USAID Pakistan to produce about 1000 Kg of ripen fruit after 3 days. The development of diferent types of solar tunnels in Pakistan was discussed in the current article. INTRODUCTION Drying or dehydration is an essential process because it is the most common method of preserving and storing the agricultural products. The dehydration process can be done through sun curing or artiicially through heat treatment using diferent types of chambers and heat supplements. Date palm is known as the most signiicant horticultural crop of Pakistan and holds a very important position in the agricultural horizon of Sindh (Marwat et al. 2012). Khairpur is the biodiversity Centre of date palm in Pakistan having more than 300 varieties (Markhand et al. 2010). Aseel is the predominant cultivar of Khairpur district and semi-dry in nature and most exported date cultivar of Pakistan (Fig. 1). Open sun drying is still widely practiced technique being used for drying unripe date fruit in Khairpur, Pakistan because of the cost and technicalities of using other alternatives. Solar tunnel technology could be the better choice which is not only eicient but also assists to maintain fruit quality (Abul-Soad 2016). Solar tunnel drying is a worldwide method for drying diferent horticultural crops by using solar energy which increases its value during of-season of date crop. Solar tunnel was tested in several countries like Algeria (Boubekri et al., 2009; Chouicha et al., 2014; Mennouche et al. 2014), KSA (Almuhanna 2012) Oman (Basunia et al. 2012) and Pakistan (AbulSoad 2016; Abul-Soad et al. 2015). However, most of the designs were with a limited capacity not enough to accommodate the Figure 2. Severe efort with unfolding mats at dawn every day to avoid night dew in open sun curing. Figure 3. Plastic tables with folded metal legs for sun curing of unripe date fruit to get hygienic product. vast amount of the fruit within a limited time of harvesting (a couple of months approximately). Not only the capacity but also easier operation to check out the temperature within the tunnel and control automatically the relative humidity through the fans. To place fruit inside the tunnel or to get it out must be with minimum efort compared to sun curing method. Using the solar energy to produce electricity for operating the fans or to produce much heat to dry out the fruit was a necessary supplement to some designs of solar tunnels at open areas that may be away from suitable source of energy. Factors controlling dehydration inside the tunnel are the temperature and relative humidity. The temperature above 55˚C may cause the burning of sugars (caramelization) and darkening the fruits. There is a range of temperatures suited to diferent date palm cultivars like Halawy requires approx. 55˚C (20% moisture remains after drying), Deglet Noor and Medjool Cvs. THE BLESSED TREE | MAY 2017 11 solar tunnel can compensate this deiciency in heat units. the Because of the importance of solar drying, Pakistan Agricultural Research Council (PARC), United States Agency for International Development (USAID) and individuals established diferent types of solar tunnel dryers in dispersed areas of the district Khairpur but unfortunately with no any prominent success due to operational and technical problems that will be discussed in the current article. Figure 4. Infestation of date fruit bunch with Dry Fruit Beetle (Carpophilus dimidiatus) caused late fruit drop before harvesting. required 50˚C (Zaid 2002). In a study on Aseel cv. fruit in Khairpur distract in Pakistan, measured temperature inside the solar tunnel during the day ranged between 51-64 C compared to outside temperature which was 15 C less and relative humidity was reduced 10% less than outside the tunnel. This diference caused fruit ripening within 2.5 days as the fruit moisture content reached 18% and associated with fruit weight loss (Mari et al. 2016). There is another factor may impact the dehydration process which is the unripe fruit stage whether ‘Khalal’, half Rutab’ with brown soft tip or ‘full rutab’. The overwhelming majority of the scientists were using ‘half rutab’ at their experiments. Growers used to pick the early ripened fruit by shaking the fruit bunch from one to three times before cutting of the bunch when about 50% of the fruit reached the ‘half Rutab’. The remaining 50% of the fruit bunch are at ‘Khalal’ stage. Sometimes, semi-dry cultivars are being planted at unsuitable areas and need more heat units by the time of harvesting to reduce the fruit moisture content. In this scenario Country like Pakistan having a hot weather has gone for sun curing (Fig. 2). But the coincidence of monsoon rains at the time of harvesting could damage whole the crop extended on mats for curing or even remained on the tree for harvesting. The only way left for the growers is to early harvest the crop in July. Early harvested ‘half Rutab’ and ‘Rutab’ fruit are extended on mats for sun curing to get dates fruit with less moisture content to be handed or stored in good quality and the unripe fruit at ‘Khalal’ stage will go to the local recipe called ‘Chohara’ by boiling. The later one is less in price than the cured dates fruit, but it is only quick way to dry out unripe fruit. The later type ‘Chohara’ is mainly exported to India. This recipe can be found in Oman as well with another local name ‘Tabseel’. It can Figure 5. Accumulating date fruit in a pile covered with mats away from light accelerated ripening process. 12 KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION mentioned that about 10-20% of total date fruit production goes for drying whereas the rest goes to make ‘Chohara’. Number of date’s factories is increasing day after day along with a need for more cured dates for processing to get better price. As a simple alternative for the mats used in sun curing, an easyfold plastic tables were ofered. There have been growing concern for hygienic product to use this subsidized easy-fold plastic tables and place unripe fruit in a single layer (Fig. 3). But using plastic tables viable alternative to the mats because of the cost, fruit moist by dew dawn and wide space occupied by these tables alike traditional mats. Figure 6. A single cemented room provided with a solar cell unit as a source for heat. There is an urgent need for getting much more cured dates in spite of monsoon rains and the limited harvesting period of time. Thus, solar tunnels were suitable option to rescue the crop. However, fossil oil, electricity and other sources of energy in Pakistan are very expensive which made no choice except to go back to the nature and use solar energy. The components of the structure were discussed as well. SUN CURING OF DATE FRUIT AT DHAKKI VILLAGE Direct sun radiation could afect the process of unripe date fruit. In a special recipe for sun curing at one of date palm centers in Pakistan, Dhakki village in Dera Ismail Khan, the date fruit covered entirely with mats for a single day to accelerate ripening process. The predominant cultivar has been given same name of the place ‘Dhakki’ cv. The overwhelming majority of trees are harvested while date fruit at ‘Khalal’ stage. Fruit can’t reach naturally the Figure 7. The dryer chamber and the metal stand of trays made from woody frame and net of wires base. ‘Rutab’ stage on tree due to the high relative air moisture (50-70%) and low temperature (30 – 38 oC). If the date fruit cop on the trees till normal ripening time makes fruit liable to severe attack of the late season pests especially the storage pests. The early ripened fruit with brown tip are tremendously infested with a particular pest dry fruit betel causing severe fruit drop (Fig. 4). This insect was detected at Khairpur too (Abul-Soad et al. 2015). Nevertheless, date palm trees at mountain range produced earlier crop and may reach Rutab stage on the tree. Growers used to cut of the fruit bunch in July and transfer them THE BLESSED TREE | MAY 2017 13 Figure 8. Solar-Cum-Gas Fired Dates Dryer installed recently by PARC. into upper mountain area for sun curing in which fruit were left for 1-2 days in sun then gathered in piles and covered with plastic sheet then with mats for a single day (Fig. 5). After then, mats were removed and more than 90% of the unripe date fruit became full Rutab and dried out. Most probably, darkness, higher temperature and capturing the moisture within the pile accelerated ripening process. The physiological changes taken place in the fruit during covering in this old recipe worth to be studied. SOLAR DRYER TYPES There was a history for the development of a variety of means to dehydrate the date fruit. All trials seemed not to have a great inluence on accelerating the dehydration process artiicially due to the above mentioned reasons. Nevertheless, presenting the diferent types of solar dehydrators and discussing the aspects of operation with suggestions to reach to an applicable and easy use design is necessity of the day. 14 THE SOLARCELL DRYER It was designed to use the heat generated by a solar unit to allow unripe date fruit to continue its ripening and reduce fruit moisture content. This type of dryers consisted of a single small room 2 meters height and about 6 square meters wide built from bricks and cement. The room painted from inside with black color and provided with a metal door to get the stands in and out. The room was connected to the second part of the dryer via a tube connect to the solar cell units (Fig. 6 and 7). The stands were made from iron and painted in black. Each stand composed of 15 shelves carrying the wooden trays (Fig. 7). Each tray loaded with about 3-4 Kg unripe date fruit. The humid air was exhausted by fan and temperature inside the dryer room was about 40-70 oC. The disadvantage of this type is the low capacity where up to 10 stands can be handled in each cycle for at least 3 days. The KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION number of inlated fruit was high due to the excess of heat inside the dryer which can’t be controlled. The overall capacity this type was less than half ton/3days. This type was installed in 2010 by Pakistan Agricultural Research Council (PARC) and wasn’t successful on the commercial side and is no more there. SOLAR-CUM-GAS FIRED DATES DRYER The previous type was updated this year by a new version through SAARC Development Fund, PARC to accommodate more fruit. Five units dispersed in diferent areas of upper Sindh in 2016. A metal-made room replaced the room made from bricks in old design and equipped with more trays to increase the capacity to accommodate more fresh dates fruit. In this room of 2×2 meters, 120 trays of wires were placed in 4 groups. This design allowed easy use to place the trays in and to get out. Also to check out the position of drying unripe fruit. Each tray loaded with a single layer of 5 Kg. The load capacity reached about 600 Kg fresh fruit. This dryer was provided with a movable window to get out the moisture and check point for the inside temperature. Therefore the dryer supported with Natural Gas unit to ensure the heat in case of decreasing the night temperature less than 55˚C. The disadvantage of this design is the manual operation for air moisture exhaust and checking out the inside temperature which is diicult to handle under the harsh weather in the month of July and August in which the temperature can reach 50˚C in the open air. No data are available about the quality of the dried fruit inside this type till the moment. Figure 9. Solar tunnel built from bricks and Bamboo sticks covered with plastic sheets. SOLAR TUNNEL MADE FROM BRICKS AND BAMBOO ARCS The high cost solar tunnels made from metal pushed the growers to think over using the available cheap materials in the nature to use it such as brick made from mud and Bamboo sticks. It is a tunnel covered with plastic sheet to keep the temperature higher than outside the tunnel and protect the drying fruit from the likelihood rain fall. The main frame was built from the bricks and ventilation windows were made in the both short side walls of the tunnel (Fig. 9). Arcs made from the elastic Bamboo sticks used to carry the transparent plastic sheet. These Bamboo sticks are widely utilized for making roofs of the houses in Pakistan. The door was made from one side and the opposite side closed with the bricks and only a couple of small windows made for ventilation. Fruit spread over the mats inside the tunnel and because of the limited capacity of such design, growers had to use Figure 10. A solar tunnel facilitated with wooden and plastic trays. the ordinary way of sun curing too. Growers weren’t satisied about this type of solar dryers in spite of the lower cost compared to other design. METAL-FRAME SOLAR TUNNEL WITH A SINGLE FRUIT LAYER This type was installed in 2011 and from this model the latest one of USAID’s irms project was developed in 2012. In fact the development process of solar tunnel dryers is endless till to get a commercial and applicable one. The current solar tunnel was built on a cemented base and the metal frame of arcs covered with transparent plastic sheet (Fig. 10). The trays made of a wooden frame and base from plastic net to avoid fruit burn when touches metal base. Trays were with short wooden legs to be placed above each other. Also, plastic crates were used as trays. But this didn’t THE BLESSED TREE | MAY 2017 15 by two meters wide (Fig. 12). Base made from wood sheets and arcs from metal and covered with plastic sheet. A thin sheet of metal has been painted with black paint and ixed in the half of this tunnel (6 meters long), but the rest of the tunnel was loaded with single layer of the fruit. As the year of 2013 was the irst year to test such design by one of the progressive growers in Sindh, diferent fruit types were successfully tested within this type of solar tunnels dryers (Fig. 13). Figure 11. Changes in the unripe date fruit during dehydration inside the solar tunnel dryer. Figure 12. The solar low-tunnel dryer. increase the capacity much and accumulated the moisture around the fruit which increased the period of drying more than 3 days. The capacity of this solar dryer was half ton/cycle of 3-4 days. Trays needs considerable efort to be arranged in 2-5 layers of trays. The lower trays required more days for fruit maturation. No fans in this type to attract the moisture from the tunnel. Ventilation restricted only on 2 small windows. The current design was found impractical like other models. 16 It is worth to mention that increasing the temperature inside the tunnel caused skin separation of the fruit instead of normal dehydration by fruit shriveling (Fig. 11). THE LOW-TUNNEL SOLAR This type used in Oman to dry out ‘half Rutab’ date fruit with capacity 180-200 Kg/cycle of 3 days (Basunia et al. 2012). The low tunnel is twelve meters long KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION The tunnels placed on stones instead of the metal legs to reduce the cost. This design recently updated by increasing the wide into double (4 meters) to increase the capacity. This design made to load and unload the fruit much easier as the unripe fruit spread over a plastic sheet. Also, it easy to check out the position of the fruit throughout the transparent plastic cover (Fig. 14). For ventilation, a fan has ixed in the empty side to push in the air which getting hot through passing above the black metal to dry out the unripe date fruit within 3-4 days. In the other side 3 windows were ixed to be opened when fax working (Fig. 15). Growers were comfortable with this design which needs source of electricity to run the fans (Fig. 16). But capacity still not within the commercial demand. SOLAR TUNNEL OF USAID’S FIRMS PROJECT This design developed in 2012 with a bigger capacity reached to 2.5 tonnes fresh fruit to produce a tone every cycle of 2.5-3 days (AbulSoad 2016; Abul-Soad et al. 2015; Mari et al. 2016). The one made from a metal frame and provided with fans to exhaust the moisture from the tunnel to outside (Fig. 17). These fans are working by solar cells to provide energy in case of insuicient electricity current. The cost is important factor that may encounter the dissemination of such solar dehydrators. Estimated cost reached a million rupees which equal to 10 thousand US Dollars. Figure 17 shows the outlook of solar tunnel dryer at Therhi area, Khairpur Mir’s, Sindh, Pakistan. This solar tunnel was made up of metal framework. The sides of the structure positioned in east to west angle (wind direction), having two exhaust fans in west side and two windows (covered with wire net) in east side to regulate the humidity and temperature inside the solar tunnel dryer. These two fans were automatically operating when the relative air moisture increased above 50% inside the solar dryer. The temperature and relative air humidity was measured by using a thermocouple. The side facing south and north was covered with a white plastic sheet. The ground within the solar tunnel dryer was covered with cement base. The electricity source to operate the fans was provided from a solar unit (700 watts). The tunnel consisted of 30 stands arranged in three longitudinal rows of 10 stands each. In each stand 7 shelves, i.e. trays. The whole frame was surrounded from outside with a short wall for protection (Abul-Soad 2016). The process of dehydration using this solar dryer is described. Figure 13. Diferent types of date fruit (Chohara, unripe Aseel and Dhakki cvs. and chopped unripe date fruit) drying within the low tunnel solar dryer. Notice the empty half of the tunnel. Figure 14. Side of the solar low-tunnel showing the black metal, arcs ixed with screw and legs of stone. DESCRIPTION OF SOLAR DEHYDRATION PROCESS INSIDE THE SOLAR TUNNEL DRYER: Artiicial maturation is a delicate, time-consuming process, and very cultivar-speciic. Taking into account also the non-stable conditions of the incoming dates from week to week and season to season, it stands to reason Figure 15. Three holes made for ventilation to exhaust the moist air from inside the solar low-tunnel. THE BLESSED TREE | MAY 2017 17 that artiicial maturation requires much practical experience by the date packer (Barreveld, 1993). The process of dehydration gone through the following steps (AbulSoad 2016): FRUIT PREPARATION Figure 16. The progressive grower who installed this design in front of the ixed fan with speed controller in the solar low-tunnel. Date fruit is preferred to be harvested at early Rutab stage compared to Khalal stage to avoid failure of fruit ripening. Early harvested fruit at Khalal stage could take more time to dry inside the solar dryer and some portion may fail to reach the desired fruit quality. The remark of the fruit at early Rutab stage is changing yellow (Aseel, Dhakki and Begum Jangi cvs.) or red color (Muzafati cv.) of the fruit tip into brown color. Fruit skin of Aseel cv. is very delicate at Rutab stage. Fruit must be handled carefully during harvesting to avoid falling the most of early ripened fruit on the ground and crush. Ground under the shade of the date palm tree is covered with a plastic sheet to collect the harvested fruit bunch and fallen individual fruit during harvest process. Figure 17. Solar tunnel dryer with commercial capacity of one tone/3 days dried date fruit. Conventional practice of date fruit harvesting is to cut and lay down the fruit bunches on the ground by aid of a rope. This practice is polluting the fruit with dust and reduces fruit quality. Conventional practice should be updated by the international better practices to use plastic sheets beneath the date palm tree to collect the harvested fruit bunch and fallen individual fruit during harvest process. Harvested fruit should be collected in the plastic crates and transferred to the place of the solar tunnel dryer by small hand carts or by trucks to the far places. Figure 18. Conventional way to detach the unripe date-fruit from the bunches on a wooden comb. 18 KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION Once date fruit reached the place of solar dryer, it should be sorted out to discard the crushed, deteriorated, mashed, infected, ruptured and shriveled fruit types before drying process. Sorting process includes dividing the fruit to three categories according to size into small, median and jumbo fruit size. It is worth to mentioning that jumbo fruit size is harvesting high prices in the market and supports the export window. Based on a preliminary study on date’s standards in the Pakistani date’s market done by Date Palm Res. Inst. (DPRI), SAL Univ., Khairpur, the category of Jumbo fruit, i.e. “A” grade consisted of 55-60 fruit/500 grams while “C” grade consisted of 75-115 fruit/500 grams package according to the general concept of fruit quality in Pakistan dates factories (Zangejo 2013). This is leading to the need to make standards for all other Pakistani date cultivars. At “Pir” or “Bethak” where loaded trucks with dates are unloaded by labor, manual fruit detachment from the fruit stalks is performed before drying inside the solar dryer, curing under sun radiation on mats or making Chohara. Fruit detachment process is done by pulling the fruit punch over a wooden comb ixed in ground (Fig. 18). It used to be a headache process due to the long time consumed to perform this process and requires considerable number of labor. An alternative solution for such process would help date palm growers to save time and reduces the end product cost could be the use of a machine. Loose fruit can’t be washed before drying in solar dryers under current practice. However, loaded fruit on the pored metal trays could be washed under running tap water for 1-2 minutes and then should be placed directly into the solar dryer at the highest tray in the stand (Fig. 19). It is prohibited to be loaded in the lower trays Figure 19. Washing the fruit before loading the trays in the solar tunnel dryer. Figure 20. A row of stands equipped with trays bearing date fruit inside the this model of solar dryer. Figure 21. The inlated fruit epicarp, i.e. skin due to higher temperature at the upper portion of the solar dryer. THE BLESSED TREE | MAY 2017 19 Figure 22. Upper trays loaded with 3-4 layers of fruit of Dhakki cv. after 3 days inside the solar dryer. or to be left for sometime after washing due high sugar content of the date fruit which encourages the fermentation process. FRUIT HANDLING INSIDE THE SOLAR TUNNEL Number of fruit layers loaded on a try is important to maximize the overall production per cycle and to avoid inlated in upper trays or rotten fruit in lower trays (Fig. 20). The highest tray is exposed to much more heat than other lower Figure 23. Sorted date fruit quality of “Dhakki” cv. after 3 days within the solar dryer. trays. Loading the highest tray with a single layer of fruit let the heat to inlate the fruit skin and then it could be exploded (Fig. 21). The swollen fruit skin separates from the beneath lesh and produces low fruit quality. However, this phenomenon was reduced when the highest tray was loaded with 3-4 fruit layers (Fig. 22). It seems that the accumulated ambient moisture of these layers reduced the negative impact of the heat on the fruit. Lower trays of a single fruit layer showed very few inlated fruit. Cold air is heavier than the Figure 24. Cured date fruit under sun radiation on mats after 5-7 days. 20 KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION hot air which increases the time required for dehydration in the lower trays. Diferent types of trays were tested. The trays were made from blind stainless steel materials caused burn for the skin. However, in the current design, trays made with bores to allow more aeration and avoid fruit burn (Fig. 23). The quality of dried date fruit inside the solar dryer (Fig. 23) were similar to those cured on the mate in open areas (Fig. 24). As intimated before, the solar dryer usage reduces the time of curing from 5-7 days into 2.5 -3 days. In Egypt, ‘Sewi’ cv. trees are growing mainly in three governorates ‘New Valley’, ‘Giza’ and ‘Al-Fayoum’ where sun curing on mats is the common practice after fruit harvesting. But, the trees cultivated outside these regions on the Cairo-Alexandria desert road where the unripe fruit after harvesting need to be transferred to surrounding areas with higher temperatures for curing. Appling this type of solar tunnel dryer could therefore be useful for dehydration at same places and in shorter period of time. These environment friendly-ways would normally be applied in similar places where the adverse climatic conditions, i.e. low temperature and monsoon rains are prevailed. Figure 25. Glazed date fruit of ‘Aseel’ cv. with vegetable oil to keep fruit moisture and to appear shiny. Not but not least, in this design, stands are lacking wheels for easy moving from and to the solar dryer to avoid opening the door for long time. Also, it recommended that fans must switch on or of automatically not manually. Third thing is to ind a mean to circulate the air inside the solar dryer upside down not only to suck the air. This may increase the capacity of this design above 2.5 tones unripe date fruit/cycle in the future. AFTER DEHYDRATION PROCESS Figure 26. Packing dehydrated date fruit in Carton containers. Figure 27. Handmade baskets for packing the ripen dates Drying fruit shouldn’t reach the full dryness less than 18% as it will lose some moisture content during handling and storage (Mari et al. 2016). Dried fruit should be loaded in plastic crates inside plastic sheets, but before that it should be kept for sometimes under shade in a protected place. Then packaged fruit should be transferred to the market or cold storage. Stored fruit in cold storage must be covered with plastic sheets to avoid further fruit moisture loss. It is a practice in Pakistan to use the vegetable oil for glazing (Fig. 25). Glazing the dried fruit with food oil changing the taste of the fruit little bit. There have diferent materials been using for packing date fruit in Pakistan. One of these materials is the carton (Fig. 26) and wooden boxes. There also were other alternative materials commonly used for ripen dates packing such as the handmade baskets (Fig. 27). The pilgrim (seasonal laborers) are coming every year a month before harvesting season starts in JuneJuly to work on date palm various activities. One of these is to make such type of baskets with diferent sizes for ripen dates packing. But, after processing of dried dates, THE BLESSED TREE | MAY 2017 21 cartoon or plastic boxes types were usually used (Fig. 28). Coming to the end, whether dried date or Chohara will go to the market for occasions (Fig. 29). Using solar tunnel dryer with Arabian cultivars that spreading now in Pakistan will help to increase the cultivated area with such elite cultivars (Fgi. 30). Price of a single Kg of Ajwa, Anmber or Sukkari cultivars A grade fruit in retail market at Karachi ranged from 1800-2200 Pak Rupees this year. The empirical references of other indicated that the lethal temperature to kill 100% of insect life is 2.5 hours at 54 °C and this time decreased to only 20 minutes, but at higher temperature 71°C (Azawi et al., 1983; 84). More or less, using the solar dryer in such a way to provide heat treatment at the level of 55-60 °C is considered as a partial pasteurization to destroy insect of all life stage, reducing the microorganisms such as bacteria, fungi and molds, and decreasing enzyme activity during prolonged storage. It was reported also that keeping the dates moisture content in the suitable range below 24% is inhibiting the redevelop of the microorganisms (Barreveld, 1993). Figure 28. A plastic box of 500 grams of whole-dried date fruit. Figure 29. Date fruit market in Pakistan. Dates sector is one of growing industries in Pakistan and during the annual festival of dates (Fig. 30 and 31) fruits of diferent cultivars were presented along with seminars to increase the awareness of the Pakistani growers. The seminar gathering all the date palm beneiciaries to discuss the emerging problems and present the new technologies. ACKNOWLEDGEMENT The author would like to express about his deep thanks to the Date Palm Research Institute, Shah Abdul Latif University, Sindh, 22 Figure 30. Fruit of diferent cultivars during the proceedings of annual dates festival at “Khairpur”. KHALIFA INTERNATIONAL AWARD FOR DATE PALM AND AGRICULTURAL INNOVATION Temperature Change. 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Rome : United Nations FAO Plant Production and Protection. 156. Rev. 1. Almuhanna EA (2012) Utilization of a Solar Greenhouse as a Solar Dryer for Drying Dates under the Climatic Conditions of the Eastern Boubekri, A.G., H. Benmoussa and D. Mennouche. 2009. Solar Drying Kinetics of Date Palm Fruits Assuming a Step-Wise Air Zangejo KM (2013) Setting Standards for Dates in Sindh. MPhill Thesis, Shah Abdul Latif University, Khairpur, Sindh, Pakistan. THE BLESSED TREE | MAY 2017 23