| The increasing demand for functional foods has boosted up the market for fiber-enriched foods that have been reported to contain elevated levels of bioactive compounds.These foods have been found with considerably high potential to decrease the risks of diabetes,arterial blood pressure,cancer,hepatotoxicity and other degenerative diseases.Doum fruit has emerged as one of the sources of dietary fiber and other nutraceuticals such as vitamins,essential minerals and antioxidants.Despite the potential of being fully utilized in the functional foods industry,there is little amount of information reported about Doum fruit.Therefore,this study was conducted in order to address the existing gap of knowledge concerning the properties of Doum fruit and fiber obtained through different processing techniques.The first objective of the study was to investigate the physico-chemical,nutritional and functional properties of Doum fruit.In order to achieve this objective,the epicarp,flesh and pitted samples of Doum fruit were processed and later,proximate composition,minerals,amino acids,fatty acids,vitamin,monosaccharide and flavor compounds were determined.Results revealed that carbohydrate contents in the flesh,pitted fruit and epicarp samples were 70.55 g/100 g,65.05 g/100 g and 44.1 g/100 g respectively.The highest contents of both total dietary fiber(TDF)and insoluble dietary fiber(IDF)were observed in epicarp samples which were(61.48 and 57.31 g/100 g respectively).On the other hand,flesh,pitted fruit and epicarp samples contained(6.92 g/100g),(6.01 g/100g)and(4.17 g/100g)SDF,respectively.It was further revealed that the fruit contained substantial amounts of essential minerals such as potassium(2947.6-806.2),sodium(364.7-184.35),calcium(284-254),magnesium(185.62-94.87),phosphorus(154.6-102.30)and iron(12.18-3.52)mg/100 g.In addition,our results demonstrated that phenylalanine and leucine were the major essential amino acids while glutamic and aspartic acids were found to be the major nonessential amino acids in all samples.Palmitic acid(C16:0)was the major saturated fatty acid and its contents in the epicarp,pitted sample and flesh were 75.10%,64.47% and 34.14% respectively.It was also observed that flesh of the Doum fruit had higher percentages(p<0.05)of unsaturated fatty acids specifically oleic(25.66%)and linoleic acid(21.39%)than the rest of the samples.In addition,Doum fruit was found to be a good source of vitamin B-complex,in particular the epicarp contented 3.6 mg/100 g niacin(B3)and 13.6 mg/100 g pyridoxine(B6).Monosaccharide content was determined by using HPAEC-PAD and the results showed that the flesh of the Doum fruit was a good source of glucose and fructose.A total of 37 volatile compounds were identified in the epicarp,flesh and pitted samples of the Doum fruit by using gas chromatography/mass spectrometry(GC/MS).Acetic acid,propanoic acid,benzeneacetaldehyde,butanoic acid,2-methyl,hexanal and hexanoic acid were the major volatile compounds in all parts of the fruit.Thus this section of the study revealed that the Doum fruit contained essential nutrients with nutraceutical functions for useful applications in the food industry.The influence of extraction method and solvent type on polyphenol and flavonoid levels of Doum fruit,as well as examine the antioxidant and antibacterial activities of the fruit extracts were also investigated in this study.The extraction procedures were performed separately in ultrasonic bath or shaking water bath.Total polyphenol content(TPC)and total flavonoid content(TFC),as well as antioxidant capacity,were maximized using methanol as the extraction solvent,particularly with the ultrasonic method.The half maximal effective concentration(EC50)values of the methanol/ultrasonic(MU),methanol/water bath(MW),ethanol/ultrasonic(EU),and ethanol/water bath(EW)extracts in the DPPH assay were 107.6,126.7,172.7,and 196.3 ?g/mL,respectively.All extracts showed a high antibacterial activity against Staphylococcus aureus and Salmonella typhi,while MU extract inhibited the growth of all pathogenic bacteria used in this study.The antioxidant and antibacterial activities of Doum fruit extracts were significantly affected by the type of extracting solvent and equipment used.Our findings further demonstrated that MU extract has higher antioxidant and antibacterial activities compared with the other extracts.Dietary fiber(DF)was isolated from Doum fruit by exploiting the alkali and microwave reactor techniques.Grinding technologies were also applied to characterize the particle size,chemical composition,structural,physico-chemical and antioxidant properties of obtained dietary fibers(DFs).Among the DF samples,MEDFSG(DF obtained by microwave extraction with superfine grinding)exhibited the highest contents of soluble dietary fiber(14.33g/100g),monosaccharides(except for xylose),total polyphenol(72.31 mg GAE/g),ABTS·+(20.09 mM TEA/100g),DPPH·(88.76%)with a crystallinity of 52.6%.Whereas,the levels of insoluble dietary fiber fractions(excluding cellulose)in MEDFSG were found to be the lowest.Furthermore,superfine grinding led to produce smaller MEDFSG particles with greater number of cracks and holes as observed by scanning electron microscopy,with improved the functional properties such as hydration properties and oil adsorption capacity as compared to its counterparts.Notably,the results revealed a novel synergistic approach of microwave reactor extraction and superfine grinding which may prove promising strategy to produce functionally active DFs for their functional applications.The fourth objective of this study was to explore applications of the Doum fruit flour(DFF)in the foods industry especially baking of bread.The Doum fruit as mentioned above,it has good nutritional and pharmaceutical properties;therefore,its incorporation in bread could be beneficial in improving human health.Partial substitution of wheat flour(WF)with Doum fruit flour(DFF)at levels of 5%,10%,15% and 20% were carried out to investigate the dough viscoelastic properties,baking performance,proximate compositions and antioxidant properties of the bread.Partial substitution of WF with DFF increased the water absorption and developing time of dough(P ? 0.05),while,the dough extensibility,resistance to extension and the deformation energy were reduced.Bread supplemented with DFF resulted in a reduction in quality in terms of specific loaf volume,conferred softness,hardness and cohesiveness to the bread crumbs.DFF up to 15 % could partially replace WF in bread;increased its nutritional value in terms of fiber content and minerals,with only a small depreciation in the bread quality.Sensory evaluation showed that bread supplemented up to 15% DFF were acceptable to the panelists and there was no significant difference in terms of taste,texture and overall acceptability compared to the control.The incorporation of DFF increased the total phenolic contents,total flavonoids contents and antioxidant properties compared to the control(for both flour and bread).In the last objective of this study,Doum dietary fiber(DDF)as described above was incorporated into biscuits.Dough biscuits were prepared using different levels(2.5,5.0,7.5 and 10%)of DDF.Farinograph characteristics of the wheat flour incorporated with DDF showed an increase in water absorption from 61.5 to 68.2%.Chemical composition,antioxidants activity,nutritional quality and sensory profile of samples containing DDF were investigated and compared with control biscuits.The total dietary fiber content increased from 1.72 to 10.23% with a high proportion of soluble dietary fiber with incorporation of 10% DDF.The content of polyphenols increased from 0.52 to 2.92 mg GAE/g DW of biscuits with 10% incorporation of DDF.The biscuits incorporated with DDF exhibited improved antioxidant properties.Acceptable biscuits with Doum flavor were obtained by incorporating 7.5% DDF.Thus,the results indicated that wheat flour incorporated with DDF yielded dietary fiber enriched biscuits with improved antioxidant properties. |
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