Somayeh Rastegar; Azam Shojaee; Behjat Tajeddin
Abstract
Introduction: Persian walnut (Juglans regia) from Juglandaceae family is one of the most important fruits in the world that has an important role in human health. It contains a notable list of plant nutrients that has been found to have disease preventing and health promoting properties. Walnut is a ...
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Introduction: Persian walnut (Juglans regia) from Juglandaceae family is one of the most important fruits in the world that has an important role in human health. It contains a notable list of plant nutrients that has been found to have disease preventing and health promoting properties. Walnut is a source of bioactive compounds such as phenolic and flavonoid complexes where they act as antioxidants and free radical scavengers. It also contains pleasant flavor and high concentration of minerals and fatty acids. Extending shelf-life of this perishable fruit has been accomplished due to its high oil level and oxidation of oil (Tajeddin, 2004). Rate of loss in walnut kernel quality and quantity between harvest and consumption affects its productivity. Control of temperature is the most effective tool for extending the shelf life of fresh horticultural products. However, to reduce high losses and keeping product’s quality, packaging method is very important as well as low temperature. Therefore, in this study, the effect of temperature (4 and 25 oC) and packaging methods (vacuum and air packaging) on the changes of walnut kernel compounds was evaluated to improve quality of its storability during six month cold storage.
Materials and methods: Walnut harvested from a commercial garden at the mountain regional of Raber, Kerman province. All chemical materials for different tests obtained from Merck Company, Germany. Immediately after walnuts harvesting, they were dehulled and dried in expose of sun shade with the circulation of natural air. The walnuts were then transferred to the laboratory and their wooden shells were removed. Subsequently, about 25 g of walnut kernel was packaged in the polyethylene films with 87μm (0.087 mm) thickness, under a vacuum machine and stored at 4°C and 25°C to be later assessed for further analyses intended for six months. Phenol, flavonoid, carbohydrate, protein, water percent, color parameters (C, h, WI), organoleptic characteristics, and peroxide value of kernels were measured every month during storage time. The control samples of packaged walnuts under environmental conditions were also stored. The current study carried out as a factorial assay on the basis of a completely randomized design with three replications at Hormozgan University. Data were subjected to ANOVA using SAS software version 9.4. Verification of significant differences was done using Duncan's Test at 1% probability level.
Results and discussion: Results showed that carbohydrate and proteins decreased during storage time. Both of vacuum package and low temperature contorted the reduction of different characteristics of kernel such as bioactive compounds during storage significantly. Sensory properties were also reduced during storage, especially at the end of period, in all conditions except for treatment at 4°C and vacuum packing. Control samples (temperature 25°C and air-containing packags) during the experiment showed a lower quality for all factors. Samples that stored in low temperature and vacuum package had better brightness (higher chroma, Hugh, lightness (L) and white index values (Wi)) than other treatments. The treatments had a significant role in the preventing of increasing peroxide value. The peroxide value in treated samples was increased from 0.023 to 0.68 meq/g, while in vacuum packages it was changed from 0.023 to 0.37 meq/g. Increasing of peroxide value was observed from 0.023 to 0.68 and from 0.023 to 0.25 meq/g in room temperature and cold temperature, respectively. After six months, the average peroxide value in all samples was less than one milliequivalent per oil kilogram. Decreasing of phenolic compounds (30%) and flavonoids (35%) and increasing the peroxide index simultaneously led to the reduction of the appearance and organoleptic properties of the control samples. Generally, vacuum package and low temperature condition that using in this study showed the best effect on the nutritional compounds quality of walnut kernel such as bioactive components during six months storage. Shelf life enhancement of walnut by vacuum packaging in the different polymers has been already reported by Tajeddin, 2004.
Marjan Haji Bagher Naeeni; Behjat Tajeddin; Gholamhasan Asadi; Babak Ghiassi Tarzi
Abstract
Introduction : Over the past 30 years with population growth, plastics have played an important role in the people's lives and its consumption is increasing. However, the most important problem of synthetic packaging materials is their total non-biodegradability that is causing environmental pollution.In ...
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Introduction : Over the past 30 years with population growth, plastics have played an important role in the people's lives and its consumption is increasing. However, the most important problem of synthetic packaging materials is their total non-biodegradability that is causing environmental pollution.In recent years, concerns about the environmental problems caused by packaging materials and plastic derived from petroleum products as well as consumer demand for qualitative food products, hascaused researchers to find alternative materials with high biodegradability, which has led to the development of biocomposites.Therefore,wheat straw-low density polyethylene composite (as a renewable material) was prepared in order to reduce the consumption of plastics in the packaging industry and the effect of two different compatibilizers, maleic anhydride polyethylene (MAPE) and polyethylene glycol (PEG) on mechanical and physical properties of obtained biocomposites was investigated.Materials and Methods: Wheat straw (WS) was first dried at 30 ℃ for 24 hours. It was then manually cut to 2-3 cmpieces manually and then was milled. The ground wheat straw was screened through 40 mesh sieve. After that, all materials including WS flour, LDPE, MAPE , and PEG were blended to prepare the different biocomposites by twin-screw extruder. The extruded materials were cut into smaller pieces proper for the next processing step by grinder.grinded. The obtained granules were then placed in the injection-molded machineto create the test samples.so combinations, respectively, were considered : WS, LDPE, MAPE (sample 1) WS, LDPE, PEG (sample 2) , LDPE (sample 3) and WS, LDPE (sample 4).Water absorption test was performed according to ASTM D 570-98 in order to study the amount of moisture absorbed by the composite samples. The samples were weighed for 9 weeks, the first time, after 24 hours, then once a week. For this purpose, samples were taken out of the water then surface moisture was dried, finally moisture absorption was calculated according to weight changes.Biodegradability test was carried out based on soil burial method for 4 monthsaccording to ASTM 6400-99. In this test, samples were taken out of the soil and washed by water every 15 days. They were thenplaced in an oven at 100℃ for 24 hours. Subsequently, samples were weighed by a digital scale with an accuracy of 0.1 mg.The amount of degradation was calculated by controlling weight changes over the time.The tensile strength, the maximum amount of force taken by a material before its failure was performed to evaluate the effect of natural fiber on the composite characteristics. It is measured with units (Pa) and (Mpa). The test was done according to ASTM D 638-08by Instron machine.The flexural strength of a material is defined as its ability to resist deformation under load. The test was done according to ASTM D790-10by Instron machine.It wasalso measured with units (Pa) and (Mpa). Result and Discussion: The results showed that the use of PEG compare with MAPE greatly increased the rate of water absorption and biodegradation of samples. It may be because of PEG's hydrophilic property that cannot act well as MAPE. Therefore, it creates an improper and weak interface adhesion between the wheat straw and polyethylene, resulting in gaps and cracks in this section. Thus, water absorption is higher in composites containing PEG. These factors also caused faster degradation in samples containing PEG. However, the use of MAPE in the composites improved surface adhesion between the wheat straw fiber and polyethylene, and therefore less water absorption and degradationwas observed.In terms of mechanical properties samples containing MAPE had greater tensile and flexural strength compared to samples containing the PEG.Because MAPE creates an ester bond in composite, which improves the interfaceadhesion of wheat straw particles and polyethylene, but when the PEG used, adhesion between wheat straw particles and polyethylene is not enough to increase the efficiency of stress transfer from the matrix to the fibers.Since almost all properties of materials are associated with each other, it cannot be introduce a combination that all properties is best. Therefore, when high biodegradability is desired, sample containing PEG is suitable but in terms of mechanical properties and resistance to water absorption, the sample containing MAPE is best combination.
