Evaluation of date kernel oils and their effects on wheat flour characteristics

En este trabajo se han utilizado aceites de pepitas de dátiles Agwa blandas y Aprimi secas. Los resultados mostraron que los aceites de pepitas de dátiles Aprimi tienen altos niveles de ácidos caproíco y esteárico, 23*04 y 18'40% respectivamente, mientras que los aceites de pepitas Agwa tienen niveles altos de ácidos caprílico y cáprico, 22'31 y 12'20%. Por otra parte los aceites Agwa alcanzaron valores elevados de materia insaponificable, esteróles y tocoferoles.


INTRODUCTION
About two hundred varieties of date are knowen of whicli only 20 are of commercial value.The annual production of different varieties of dates in Egypt exceeds 126 million tons.
Dates contain high level of inverted sugars together with relatively low fat content which are considered a rich source of calories.
Moreover, Majumdar et al (1986) studied the nutritional quality of fractioned randomized palm oil using rats and achieved that fractioned randomized palm oil can be regarded as a better dietary fat.Boiling et al. (1973) and Mostafa (1982) improved the loaf volume and rheological properties of wheat flour dough by using oils as additives.
The purpose of this study was to estimate the biochemical properties of date kernel oils to use it as human nutrient and to investigate its effects on the physical characteristics of dough.

MATERIALS AND METHODS
Two samples of palm date were obtained from the local market.These samples were Agwa soft date and Aprimi dry date.
The kernels of these dates were separated from dates manually.The obtained kernel samples were ground to pass from 20 mesh, and then kept in tight containers in refrigerator at 3°C for analysis.
The resulted ground samples were subjected to fat extraction by using hexane according to the method described in A.O.A.C. (1975).Oils extract was saponified (A.O.A.C, 1975) and the unsaponifiable matters were separated.Hydrocarbons were isolated and determined by a column chromatography as outlined in A.O.A.C. (1975).Sterols were extracted and determined according to Emmerie and Engel (1939).Tocopherols in the unsaponifiable matters were colorimetericaly assayed following the method of Emmeri and Engel (1939).Acid, saponification and iodine values and refractive index were determined as detailed in A.O.A.C. (1975).Identification and determination of fatty acid contents in the oils of date kernels were determined by gas liquid chromatography after conversion to their methyl esters according to the method of Burchfield and Starrs (1962).Date kernel oils, Agwa and Aprimi, were added at ratio of 0.06%, 0.24% and 0.64% to wheat flour.
Wheat flour (72% extraction) was purchased from Mill and Bakery Co., Cairo, that was imported from France.
Dough mixing properties were obtained with Farinograph according to the method described in A.A.C.C. (1975).Dough resistance and extensibility assessed with Extensograph using flour dough containing 1% sodium chloride according to the defination in A.A.C.C, (1975).

RESULTS AND DISCUSSION
According to the data shown in table I, dry date kernels Aprimi had high fat levels: 7.75% and low moisture: 4.33% in comparison to that of soft date Agwa kernels.The composition of fatty acids shown in table II showed that the short chain fatty acids are present in higher amounts; i.e. caproic acid and caprylic acid in levels: 23% and 22.31% in Aprimi and Agwa date kernel oils respectively.Moreover, Aprimi date kernel oil contained linoleic acid and linolenic acid in higher percentages; 8.17% and 8.17% respectively  when compared to Agwa date kernel oil, 0.95% and 3.62%, respectively.The unsaponifiable matter contents presented in table III showed that Agwa date kernel oil had high contents of unsaponifiable matters and hydrocarbons; 7.14% and 4.29% respectively.Aprimi date kernel oil contain high sterols; 2.96%.
These figures are higher than what was reported by United States, Department of Agriculture (1987), Piskur (1968), Benifort and Naria (1965) and Bailey (1946) add that may be due to variety differences of dates.
The physical and chemical properties of Agwa and Aprimi date kernel oils are shown in table IV.The refractive index was used for the determination of the degree of unsaturation.The difference in values were in the third decimal point.Aprimi date kernel oil has the highest acid value and iodine number, 0.88 and 15.49 while Agwa date kernel oil has the highest saponification number 148.32.The low iodine values were attributed to low content of unsaturated fatty acids.These results obtained were in agreement with those of Bailey (1946).
Table V shows that the addition of Aprimi dry date kernel oil at any level to wheat flour 72% extraction decreased the water absorption more than the addition of Agwa date kernel oil.Also the addition of Agwa and Aprimi oils did not improve the dough quality as the dough development time and dough stability were decreased.It is clear from this table that the addition of soft and dry date kernel oils weakened the wheat flour as the weakening values raised.
The data mentioned in table VI indicate superiority of the addition of Agwa soft date kernel oil at 0.064% level to wheat flour as it had the high resistance to extensibility compared with the other two levels and to the Aprimi dry date kernel oil at the levels used in this study.It therefor could be concluded that palm date kernel oil is rich in saturated fatty acids and sterols that are plant sterols.
As quoted by Department of Agriculture (1987) that palm date kernel oil is among the most highly saturated and artery-damaging fats known, so this fat should not be used commercially in such foods as cookies, cakes, doughnuts, cereals and nondairy creamers.

Table I
Fat contents in date kernels.

Table II Fatty
acid contents in date kernel oils.
Table III Unsaponifiable matter contents in date kernel oil.