Scientific Team

Prof.Dr Awad M. Hussein
Professor of Post Harvest Physiology & Pomology,
University of Alexandria, Egypt

Eng. Hasnaa Harrak
Researcher,
National Institute for Agricultural Research, Marrakech, Morocco

Eng. Habib Bouabidi
Researcher,
Date Palm Center Dguach, INRAT, Tunisia

Development / Improvement of Date Palm Postharvest Handling

Awad M. Hussein

Alexandria Postharvest Center (APHC)

Fac. of Agric., Alex. Univ. Alex. Egypt

Abstract

Dates (Phoenix dactylifera. L.) were and still are an important crop in the Arabian peninsula (AP). Many advances have been made in the date palm culture and the fruit are processed, shipped and enjoyed throughout the world. However in some date growing areas there is more room for improvements of the industry. Harvesting, Postharvest handling and processing, storage and food safety considerations need to be reviewed and await more development Postharvest ripening procedures currently applied and possible ways to improve it, organically produced dates and value added treatments will be presented. In the present paper such issues are addressed and related problem solving research approach is proposed.

Keypoints in the presentation

Khala

· The fruit starts to turn yellow or red .

· Now it is botanically mature

· weight gain is slow

· sucrose content increases

· moisture content goes down

· tannins will start to precipetate and loose their astringency

· Khalal may become palatable at that stage and considered commercially mature

Rutab

· Tips of the fruit starts to turn brown and rutab stages sets

· Decrease in weight due to moisture loss

· Sucrose invert sugars

· Browning of the skin

· Softening of the tissue

· Moisture content goes down to about 35%

· Dates at this stage are sold as fresh fruit

Tamar

· When dates are left to ripen further on the palm they will turn into tamar if climate conditions permit

· Moisture content makes date self-preserving

· The upper limit for the date to be self-preserving is around 24-25 %

· Dates distinguish them selves from most other fruit in that they have a botanical maturity and at least 3 distinct commercial maturation levels the sweet khalal , the rutab and the tamar .

Date qouality profile

· Color, shape, size, taste, texture, pit / date ratio and uniformity in color and size of the fruit

· Moisture, sugar and fiber content

· Defects of the fruits discoloration , broken skin , sun burn , blemishes , shrivel , deformity , etc…….

· Presence of insect infestation, foreign matter, pesticide residues, mold and decay

Insect infestation

· Storage insects if left uncontrolled can devastate the date, materially, and organoleptically.

Insect development in storage

· High initial degree of infestation prior to storage ,(eggs)

· Elevated temperatures and humidity of the air .

· Higher moisture level of date .

10 points to justify using machinery in Dates

1-The date palms must be widely spaced .

2- The palms must be planted in straight line .

3 – The palms must be adult

4- The palms must be about the same age.

5- The palms should preferably be all the same variety .

6- There must be no interplanting.

7- There must be no deep , open drains or water channels to be crossed.

8- The yield should be heavy , if the machine is to pay.

9- The dates must be dry or nearly so.

10- Labour must be expensive and machinery relatively cheap .

Prevention and control can consist of

· keeping down or eliminating initial contamination,

· fumigation, either atmospheric or under vacuum,

· lowering storage temperature and regulating humidity of the air,

· lowering moisture content of the' date, if consistent with quality retention,

· heat treatment of dates prior to storage,

· compressing dates to inhibit insects to penetrate or eggs to hatch.

Definition of defects

· Blemishes scars, discoloration, sunburn, dark spots, blacknose or similar abnormalities in surface appearance affecting an aggregate area greater than that of a circle 7 mm in diameter.

· Damaged (Unpitted dates only )- dates affected by mashing and/or tearing of the flesh exposing the pit or to such an extent that it significantly detracts from the visual appearance of the date

· Unripe Dates Dates which may be light in weight, light in colour, have shriveled or little flesh or a decidedly rubbery texture.

· Unpollinated Dates Dates not pollinated as evidenced by thin flesh, immature characteristics and no pit in unpitted dates.

· Dirt Dates having embedded organic or inorganic material similar to dirt or sand in character and affecting an aggregate area greater than that of a circle 3 mm in diameter.

· Insects and mites damage and contamination Dates damaged by insects or mites or contaminated by the presence of dead insects or mites, fragments of insects or mites or their excreta.

· Scouring Breakdown of the sugars into alcohol and acetic acid by yeasts and bacteria.

· Mould presence of the mould filaments visible to the naked eye.

· Decay Dates that area in a state of decomposition and very objectionable in appearance.

Darkening

Darkening of dates beyond the natural light to dark brown colour at harvesting is caused by several mechanisms

- enzymatic oxidative browning (polyphenolase)

-non-enzymatic oxidative browning by involving the more complex tannins

Allowance for Defects

· The maximum allowances for the defects defined above shall be

· A total of 7%by count of dates with defect blemishes

· A total of 6% by count of dates with defects damaged, unripe and unpollinated

· A total of 6% by count of dates with defects dirt and insects and mites damage and contamination

· A total of 1% by count of dates with defects scouring and mould and decay

Preventive measures are

· to keep initial microbe counts down as much as possible

· lowering storage temperature

· keeping moisture levels down, if consistent with quality desired

· storing dates in adjusted relative humidity of the air in order they will not increase in" moisture content

· compressing dates to exclude oxygen and making them impenetrable

· heat treatment

· use of anti-microbial agents

Lot Acceptance

A lot will be considered as meeting the quality criteria requirements of the standard when

· there is no evidence of live infestation and

· the sub-sample, as taken in conformity meets the general requirements , and does not exceed the allowances for the respective defects, except that with respect to size requirements, 5% ( 5 dates out of 100 ) may weight less than the specified minimum.

Future Research and extension Topics needed

Following the well established rule

The quality of the crop is made in the field and the objectices of the postharvest activites are

1- To maitain the quality

2-Reduce losses

3-Provide food safety

The topics may include

· Development of good data base for date growing and marketing in the region

· Develop a guide for who is who in date indsry in the region and strengthen a date network.

· Develop good research plan (problem solving research) and , varietal selections.

· Date oriented extension program will benefit from the execting facilities to develop an expert system outreach with good attention to small-scale growers and marketers.

· Emphasis should be given to date harvest, postharvest handling, proceesing and marketing.

· Food safety and sanitation issues should be addressed

insect infestection and reinfestation

Pathogenic disorders.

· Development of alternative methods of disease and

· Insect control to provide food safety .

· connect the date research stations and improve coordination among them within country and among countries.

· Improve packaging and develop new package to surve the market .

· Promote dates in new markets

· Cooperate with food techs. To develop more new products from different classes of dates

Date Tips/watch your step

· The European Union (EU) is a key market for date exporters. Although the EU imports of dates repersent only 10 percent of world imports in volume, they account for some 30 percent in value. This refelects the fact that EU prices for dates are comparatively much higher than the world average.

· The tendency of consumers to shift towards higher quality products, ther seems to be little scope for a large increase in exports of common dates to EU.

· Any country wishing to enter the EU date market would need to turn to"non-traditional varieties". Medjool seems to be the most promosing.

· The value of EU imports has been relatively stagnant over the last decade and import prices have declined since 1996. It is important that exporting countries find new date products that could increase the value of their exports.

· There is room for increased imports of the deglet Nour dates (or other varieties with similar taste and texture) provided high standards od quality (including low infestation rate), packaging and traceability could be met.

· Medjool has attracted major interest the United Kingdom and France and and fetched high prices.

· The potential for Hayani and Barhi seem limited to a small ethinic market. Large-scaler retailers seem reluctant to carry Hayani dates due to the fact that it is a frozen product.

· France, United Kingdom, Germany, Italy and Spain account for 85 percent of total EU imports of dates in volume. Imports by the other 10 EU member states account for 15 percent only.

· Tunisia with a market share of 48 percent and Algeria with 20 percent are the EU's main suppliers.

· Processed dates are generally more popular than natural dates. It is estimated that 55 percent to 60 percent of the imported dates are processed. There are many different types of packaging in the EU (punnets, bags, ravier, tub, glove boxes, window boxes) and the 5-kg bulk is common to every country.

General Remarks.

· Methyl bromide fumigation (40 – 100 mg / liter for 2hr.)did not significantly change protein or major sugar contents of DN dates.

· Dates should be analyzed for residues of bromides before dates are passed for human consumption.

· Methyl bromide fumigation for disinfection is a very effective quarantine treatment (dose and time).Instantaneous, nondestructive moisture content sensing technique (std. error about %) is recommended for further development.

· Date firmness correlates well with grade standard, moisture content, and water adsorbability during hydration and consumer appeal.

· Fresh dates (Samani and Zaghloul) were best stored at 5 – 7°C + 80 – 85% RH.(other sources indicate that 0 °C is better )

· Frozen (-20°C) them thawed fresh dates of Samani , Gaghloul and Bent Aisha Showed a sharp increase in the activity of peroxidase between 6 and 18 hrs. after thawing them either fill (Bent Aishfel and Samany) or rose slightly (Zaghloul). Polyphenoloxidase and pectin methyl esterase showed marked activity after thawing. Postharvest freezing could be a rapid commercial method of inducing rutab- like dates with good consumer acceptance (off season).

· A whitish film of sugar crystals may form on the surface of date fruit during storage and makes packing difficult. This is due to solubilization of glucose and fructose in the moisture of the date and their migration to the surface. Film wrapping of the stored date will reduce the problem of moisture permeability through the date skin.

· Dates stored with other aromatic products are likely to absorb the flavors of such products. Avoid storing dates with apple, onions or potatoes in ordinary cold storage. Avoid storing dates with meat in frozen food storage.

· Storage temperature and moisture are important in limiting the storage life of dates.

· Storage of dates at 0°C or lower for months very substantially reduces the population of yeasts, molds and bacteria but a complete kill is not accomplished. Upon return to favorable temperature the surviving organisms resume activity and may cause spoilage under suitable conditions.

· Respiration rates of ripe date are low Small fraction of total oxygen absorbed and carbon dioxide produced is associated with the true respiration.

· Growing molds, yeasts and bacteria on the surface of the dates increase the apparent rate of respiration. Seed respiration accounts for one fifth of gas exchange in whole fruits.

· Experimental Postharvest Ethephon application enhanced ripening of Hayani fresh dates (khalal). Reduction of tannins was reported in response to the treatment. In another work, acidity increased in treated dates.

· The degree of methylation of date pectin affect the texture of the dateSoft (tamar) 39% Hard Kimri 72%.

· The peak of ethylene production proceeded the climacteric peak (7 day in Hillawi date).

· Storing Madjool date at 0°C and – 18°C showed bright yellow – brown spots of crystallized solutes. At -35° to - 50°C the injury was not detected. The injury may be attributed to the damage of cell membranes and cell walls at the higher range (0 to - 80°C ).

· There is dose dependent inhibition of superoxide and hydroxyl radicals by an aqueous extract of date fruit. Results indicate that antioxidant and antimutagenic activity in date fruit is quite potent and implicates the presence of compounds with potent free-radical scavenging activity.

· Mold cause large losses before and just after harvesting if rain or high humidity occur at that time. Aspergillus, Alternaria, and Penicillium are of concern. High moisture dates are more subject to molds than dried ones in general.

· Dates attacked by yeasts can be detected by alcoholic odor or white aggregates in skin cracks in fermented dates.

Non-pathological disorders in dates

· Dates may darken, become syrupy, develop sugar spots, lose flavor, become too dry or too moist or develop objectionable granular texture. High temperature and high moisture content enhance sugar inversion (Sucrose Glucose+ Fructose).

· Date darkening depends on temperature, moisture content and it is a result of oxidative and non-oxidative reactions.

· Oxidative reactions can be reduced by storage in inert gas or vacuum. Darkening may be reduced by lowering storage temperature and reducing moisture content.

· Sugar spotting lower date marketing value rather than making them inedible. Spotting may be removed by gentle heating but may reappear on standing. Sugar crystals on the date surface are known as "Sugar bloom" they can also be removed by gentle heating.

· Soft cultivars have different tendency to form sugar spots. Semidry and the dry contain large amounts of sucrose and have fewer tendencies to form sugar spots.

Selected referances

· Abbas, M. F., and M. A. Ibrahim. 1996. The role of ethylene in the regulation of fruit ripening in the Hillawi date palm (Phoenix dactylifera. L.). J. Sci. Food Agric. 72306 – 308.

· Ahmed, A. I., A. W. K. Ahmed, and R. K. Robinson . 1995. Chemical composition of date varieties as influenced by the stage of ripening. Food Chem. 54 305 – 309.

· Aziz, A. B., S. M. El-Nabawy, F. K. Abdel-Wahab, and A. S. Abdel-Kader. 1975. Keeping quality of fresh date fruits as affected by cultivar and storage temperatures. Egypt. J. Hort. 1678- 74.

· Barreveld , W . H 1993 Date PALM PRODUCTS

· Fao agricutural services bulletin no.101

· Dull, G. G., R. G. Leffler, G. S. Birth, A. Zaltzman, and Z. Schmilovitch. 1991. Hortiscience 10 1303 – 1305.

· El-Sayed, S. A. 1978. Control of Post-harvest storage decay of soft-type date fruits with special refernce to the effect of gamma irradiation. Egypt. J. Hort. 2175-182.

· Hassaan, I. M., M. G. El-Sheemy. 1989. Freeze- thaw bio-chemical changes in three Egyptian date varieties. Annals. Of Agricultural Sci. (Cairo). 1 205 – 222.

· Kamal, H. M. 1995. Effect of cold storage temperatures on storability and quality of date palm fruits. Bulletin of faculty of Agric., Univ. of Cairo. 2 265 – 267.

· Khalfia, A. S., A. A. M. El-Hammady, M. M. El-Hammady, andWally, Y. A. 1975. Ripeningof date fruits as affected by ethephon. Egypt J. Hort. 2 83 – 102.

· Myhar, R. M. A. A. Alawi, J. Karkalas, and M. S. Taylor. 2000. Sensory and textural changes in maturing Omani dates. J. Sci. Food Agric. 80 2181 – 2185.

· Nelson, S. O., and K. C. Lawrence. 1994. Rf impedance sensing of moisture content in individual dates. Transactions of ASAE. 3 887 – 891.

· Oubahou, A. A. and E. M. Yahia. 1999. Postharvest handling of dates. Postharvest News and Information 10 (6)67N- 74N.

· Rouhani, I. and A. Bassiri. 1977. Effect of ethephone on ripening and physiolgy of date fruits at different stages of maturity. J. Hort. Sci. 2289 – 297.

· Rygg, G. L. 1975. Date development, handling, and packing in the United States. Agric. Handbk. 482, Agric. Res. Service, U. S. Dep. Agric., Washington, D. C.

· Salem, H. 1995. Migration of sugars in Tunisian cv. Kenta de Gabès dates. Fruits (Paris) 50 293 – 297.

· Schmilovttch, Z., A. Zaltzman, A. Hoffman, and Y. Edan. 1995. Firmness sensor ans system for date sorting. Applied Engineering in Agriculture. 4 555 – 560.

· Shomer, I. , H. B. Neori, B. Luzki, and U. Merin. 1998. Morphological, structural and membrane changes in frozen tissues of Madjhoul date (Phoenix dactylifera. L.) fruits. Postharvest biology and Technology. 14 207 – 215.

· Vayalil, P. K. 2002. Antioxidant and antimutagenic properties of aqueous extract of date fruit (Phoenix dactylifera. L. Arecaceae). J. Agric. Food Chem. 50610 – 617.

دراسة مج البخار المائي عند تمور "دقلة نور" التونسية

حبيب البوعبيدي و عبد القادر نبيلي

المعهد الوطني للبحوث الزراعية بتونس

مركز البحوث في النخيل و التمور 2260 دقاش تونس

Abstract

In Tunisia, “Deglet Noor” is the most important dates exported abroad. About 80% of these dates are exported after being treated inside packaging units which the majority are still following traditional methods. Thus, it requires more efforts to review these methods, especially drying ways for more efficiency, low cost and optimising best conditions to preserve dates quality in storage. For that purpose “Sorption Isotherms” were designed for “Deglet – Noor” dates at 5, 30 and 40 °C and were described by the theorical model of GAB. Parameters and constants of this model and moisture content in the monomolecular layer were evaluated. The necessary drying energy and shelf life were discussed.

ملخص

بالبلاد التونسية تعتبر التمور من أهم المواد الفلاحية المصدرة إلى الأسواق الخارجية و يعتبر الصنف "دقلة النور" من أصناف التمور الأكثر شهرة و الأكثر تصديرا. حوالي 80 بالمائة من هذه التمور يصدر بعد معاملتها داخل وحدات التكييف التي لا يزال العديد منها يتبع أساليب شبه تقليدية مما يحتم بذل المزيد من الجهد للسيطرة على الطرق المتبعة, و خاصة عمليات التجفيف, وجعلها أكثر جدوى و أقل كلفة و كذلك التحكم في الظروف المناسبة للمحافظة على نوعية التمور أثناء الخزن.

لذلك تم تصميم منحنيات مج البخار المائي متساوية درجة الحرارة لتمور "دقلة نور" على درجات حرارة 5 , 30 و 40 درجة مئوية و تم وصف هذه المنحنيات بمعادلة GAB كما تم تقييم ثوابت هذه المعادلة و محتوى طبقة الامتصاص الأولى من الماء. حسبت الطاقة اللازمة للتجفيف والعمر الافتراضي لهذه التمور.

1 - مقدمة

تعتبر التمِور الركيزة الأساسية في الحياة الاقتصادية لمساكني الجنوب الغربي التونسي (1), كما تمثل أهمية بالغة بالنسبة للاقتصاد الوطني بحيث تمثل 13 بالمائة من قيمة الصادرات الفلاحية (2). يمثل الصنف "دقلة نور" حوالي 80 بالمائة من الصادرات التي بلغت 42000 طنا خلال موسم 2002 – 2003. كل الكميات المصدرة تمر عبر محطات التكييف بحيث يخضع قسم كبير منه (80 بالمائة) إلى عمليات التبخير و التنظيف والفرز والتليين والتجفيف و الخزن.

ورغم أن عدد وحدات التكييف قد ازداد بشكل ملحوظ غير أن طرق العمل لا تزال شبه تقليدية في العديد منها. ذلك بأن العمليات الأساسية وهي التليين والتجفيف لم تحض بالدراسات اللازمة لجعل التمور المعاملة قابلة للتخزين لفترات طويلة. فمن المعلوم أن النشاط المائي عند التمور أو أي مادة غذائية بصفة عامة له علاقة مباشرة بقابلية هذه المواد للتخزين و سلامتها من التلف ( 6 ).

من أجل ذلك ظهرت الحاجة الماسة لدراسة العوامل المأثرة على نوعية و جودة التمور المخزنة ومنها محتوى هذه التمور من الماء, درجة حرارة الخزن, نسبة الرطوبة في أماكن الخزن. تم تصميم منحنيات المج متساوية درجات الحرارة لصنف "دقلة النور" المتأتية من واحات الجريد التونسي على درجات حرارة مختلفة واستعملت معادلة (GAB) لتمثيلها و وصفها.

2 - المواد والطرق

2-1 التمور

استعملت تمور من صنف "دقلة نور" من واحة دقاش بالجريد التونسي أثناء موسم الجني.

2-2 محتوى التمور من الماء

تم تحديد محتوى التمور من الماء بوضع عينات بالفرن على 70 درجة مئوية و لمدة 72 ساعة

2- 3 محتوى التمور من السكريات

تم تحديد محتويات التمور من السكريات باستخدام محاليل انزيمية من

مخابر BOEHRINGER MANNHEIM و قراءة على جهاز SPECTROPHOTOMETRE MILTON ROY SPECTRONIC 401 على طول موجة 340 نانو متر.

2- 4 تقييم لون التمور

تم تقييم مقاييس لون التمور باستخدام جهاز Chromametre Minolta CR300 و باعتماد مكونات اللون المصادق عليها من طرف اللجنة العالمية للإضاءة (CIE, 1976) والمكون من ثلاث مقاييس وهي L و يمثل اللمعان (من 0 % أسود الى 100 % أبيض), a من 60- وهو الأخضر الى 60 وهو الأحمر و b من 60- وهو الأزرق الى 60 وهو الأصفر.

2-5 تصميم المنحنيات

2-5-1 المحاليل الملحية المشبعة

تم تحضير محاليل ملحية مشبعة داخل أوعية زجاجية سعة لتر و مجهزة لتغلق بإحكام بحيث لا تتفاعل مع المحيط الخارجي. و حسب درجة الحرارة التي تتواجد بها تعطي هذه المحاليل قيمة مغايرة للنشاط المائي (a_w) كما هو مبين بالجدول التالي حسب (5)