Effects of particle size and moisture content of maize grits on physical properties of expanded snacks

The main aim of this research was to investigate the effects of simultaneous changing of maize grits particle size and moisture content on some physical properties and microstructure of the expanded snacks produced by an industrial single screw extruder. Maize grits with different particle sizes of 212–299, 300–474, 475–680, 681–870, 871–1,016, and 1,017–1,070 μm and various moisture contents of 15, 16, 17, and 18% were used to manufacture puffed products. The samples produced with larger particle sizes and higher moisture content exhibited lower water absorption and water solubility indices and less expansion and crispiness than other samples. As microstructure results revealed, these samples showed more uneven surface and thicker cross‐section. Overall, controlling both moisture content and particle size of maize grits had significant effects on the quality of the snacks. However, the impact of changing particle size on the snack properties was greater than changing the moisture content. This research has implications in food industry in production of puffed snacks using extrusion process. The results provide practical and green methods of improving the quality of the snacks by choosing the appropriate feed particle size and moisture content. The approach introduced in this paper is easy to impediment in the food industry without the need to change extruder configuration or adding to the list of ingredients and additives.     

Development of extruded snacks using taro (Colocasia esculenta) and nixtamalized maize (Zea mays) flour blends

Extruded snacks were prepared from flour blends made with taro and nixtamalized (TF-NMF) or non-nixtamalized maize (TF-MF) using a single-screw extruder. A central composite design was used to investigate the effects of taro flour proportion in formulations (0-100 g/100 g) and extrusion temperatures (140-180 °C) on the following indices: expansion (EI), water solubility (WSI), water absorption (WAI) and fat absorption (FAI). Moreover, selected TF-NMF and TF-MF extruded products were partially characterized through proximate chemical analysis, resistant starch, color, pH, water activity, apparent density, hardness, and sensory analysis. Results indicated that EI and WSI of both TF-MF and TF-NMF extrudates were significantly increased by the use of higher proportions of taro flour, while the opposite behavior was observed for the FAI (p < 0.05). Taro flour at higher proportions in both extrudates did not produce a significant change of WAI, while the use of higher extrusion temperatures only caused a significant increase of FAI in TF-MF extrudates (p < 0.05). This study showed that flour mixtures made from taro and nixtamalized maize flour produced puffed extruded snacks with good consumer acceptance.     

Development of healthy extruded maize snacks; Effects of soybean flour and feed moisture content

The main aim of this research was to introduce a green and clean method of increasing the nutritional quality while preserving the quality of extruded maize snacks. This was achieved by addition of soybean flour (5%, 10%, 15% and 20%, w/w) as a source of plant protein, fibre and bioactive compounds and changing the feed moisture content. Extruded samples were produced using a single-screw extruder. Increasing the soybean flour and feed moisture content resulted in reduced specific mechanical energy of the extruder and consequently several changes in physicochemical properties of the snacks including higher moisture content, lower expansion and volume, reduced crispiness, reduction in L-and a-values but an increase in b-value and formation of more wrinkly and thicker air bubbles cell walls as observed under scanning electron microscope. The addition of <20% soybean flour and feed moisture content resulted in snacks with improved nutritional value and physical properties.     

Physicochemical properties of ready‐to‐eat extruded nixtamalized maize‐based snacks enriched with grasshopper

The aim of this research was to prepare an extruded snack based on nixtamalized maize flour (Zea mays L.) (NMF) enriched with grasshopper meal (Sphenarium purpurascens Ch.) (GM) using a single screw extruder with a compression screw ratio of 3:1. A central experimental design comprising three independent variables, namely, extrusion temperature (T = 120–180 °C), feed moisture content (FMC = 18–22 g/100 g) and the grasshopper meal proportion (GMP = 0–40 g/100 g), was used. Increasing T decreased (P < 0.05) the expansion index (EI), bulk density (BD) and hardness (H). Increasing the FMC increased (P < 0.05) the EI. Increasing the GMP decreased (P < 0.05) the EI, H and water absorption index (WAI) and increased (P < 0.05) the BD and total colour difference (ΔE). The treatments that resulted in better general acceptability were those that contained a lower GMP. An extruded snack acceptable to the consumer can be obtained from a blend of NMF and GM, and up to 8.11 g/100 g of GM can be incorporated without affecting the physicochemical properties and acceptance of the snack.     

热碱浸泡玉米粉的热力学特性和流变学特性

为了解热碱浸泡技术对玉米粉热特性以及流变特性的影响,测定了热碱湿磨玉米粉和湿磨对照玉米粉的DSC、RVA和流变参数。结果表明:热碱湿磨玉米粉的起始温度、糊化温度较高,但糊化焓值较低;黏度曲线显示热碱处理样的峰值黏度、谷值黏度、最终黏度和回生值都低于湿磨对照玉米粉;两种玉米粉均为假塑性流体,且热碱湿磨玉米粉表现了较好的剪切稳定性,在两种玉米糊凝胶结构里,弹性特征更为重要。     

Micromechanical properties of almond kernels with various moisture content levels

Almond fruits are subjected to various mechanical stresses throughout production, from harvest to processing, storage and packaging. Kernel properties play an important role in reducing mechanical damage such as scratches and penetration of shell pieces. Knowledge of kernel properties under various conditions of the fruit can assist in optimising post-harvest and processing lines to minimise kernel damage and thus maximise final kernel quality. Kernel moisture content is one of the main attributes affecting the kernel’s response to mechanical processing. Increasing the kernel moisture content to an optimum level through wetting fruit prior to processing can lead to a reduced percentage of damaged kernel. Water added to the structure of kernels acted as a plasticiser and helped the kernels to absorb the mechanical load instead of fracturing and breaking into pieces. In this study, tests were conducted on almond kernels with different moisture content levels from 5.52 to 14.09g/100g wet basis. Kernels from a Nonpareil variety were tested in dried and wetted conditions. Test results showed that kernels with higher moisture content were able to undergo a larger deformation at a given force value in comparison with dry kernels. Average deformation for dry samples was from 0.12 mm, which increased to an average of 0.25 mm in wetted samples. The effect of skin on the mechanical properties of the kernels (with and without skin) was studied using a mechanical tester. The test results showed a peak force value in samples tested with skin in comparison with the kernels tested without skin.     

菜籽油中类胡萝卜素含量的影响因素及其抗氧化作用

类胡萝卜素为脂溶性化合物,在菜籽油中含量丰富。为提高菜籽油的营养价值和氧化稳定性,对菜籽油中类胡萝卜素含量的影响因素进行了分析,并对类胡萝卜素的抗氧化作用研究情况进行了综述。油菜籽品种以及加工工艺会影响菜籽油中的类胡萝卜素含量,而菜籽油中类胡萝卜素含量的提高,可以增强菜籽油的氧化稳定性。可通过转基因技术培育高类胡萝卜素含量的油菜籽品种,对油菜籽采用焙烤、微波等热处理和不脱皮的预处理方式,以及适度精炼等方法提高菜籽油中的类胡萝卜素含量。     

Non-isothermal autohydrolysis of nixtamalized maize pericarp: Production of nutraceutical extracts

Nixtamalized maize pericarp (NMP) was subjected to isothermal processing in aqueous media, and the amount and composition of the solid and liquid phases were determined. The major reaction products were arabinoxylo-oligosaccharides (AXOS). The maximum release of AXOS (39.6 g/100 g NMP) was achieved operating at 207 °C. Ferulolyl substituents of AXOS accounted for 77% of the total ferulic acid contained in the feedstock. Autohydrolysis liquors were extracted with ethyl acetate, and the phenolic compounds present in the organic phase were identified and quantified. The antioxidant activity of extracts (measured by reducing power and radical scavenging activity) compared favorably with the ones of commercial antioxidants. On the basis of the experimental results, it can be concluded that the obtained feruloylated AXOS can be used as food ingredients with potential to cause health benefits (including prebiotic effects and prevention of harmful oxidation reactions).     

玉米生霉粒和霉变粒与真菌毒素含量关系的研究分析

玉米生霉、霉变和玉米中的真菌毒素都是真菌作用的结果,为了探究玉米生霉粒、霉变粒与真菌毒素含量之间的相关性。本研究选取了江苏、河北、辽宁等17个省(市)1 300多份玉米样品,研究了玉米生霉粒和霉变粒与真菌毒素含量之间的关系。结果表明:不同的地区的玉米籽粒生霉、霉变率与真菌毒素含量高低有一定的差异,玉米籽粒生霉粒和霉变粒含量与真菌毒素的含量之间没有正相关性,不能通过感官检验玉米生霉粒和霉变粒情况,来判断该玉米真菌毒素含量的高低,这表明,要确证真菌毒素的含量还必须用专业仪器设备进行定量检测。     

Physical analysis of friction cooked RTE snacks

Extrusion is widely applied for production of ready to eat snacks. The existing technology is capital intensive and requires preconditioning the raw grains before extrusion, dedicated drying after extrusion and post extrusion addition of fat and sugar where required. A novel technology, friction cooking, has been developed to greatly lower capital costs and overcome the limitations of conventional extrusion. The production conditions (temperature and moisture content) and resulting physical properties from eight friction cooked raw grains were compared to the equivalent properties of conventionally extruded products from these grains. Properties were expansion ratio, bulk density, hardness and colour. Friction cooking temperatures were lower (60–98 °C versus about 150 °C), and products were softer but with a lower expansion ratio and higher densities. In friction cooking colour differences between raw grains and cooked product were minor. Many of these differences were attributed to lower temperatures and moisture contents in the friction process.     

Studies on the usefulness of Cucurbita maxima for the production of ready-to-eat dried vegetable snacks with a high carotenoid content

Recent research indicates a beneficial influence of a diet rich in β-carotene on human health. For that reason, experiments were undertaken to process winter squash with a high carotenoid content into ready-to-eat dried snacks. Sensory quality and dietary value of chips and crispy cubes made from different cultivars were investigated.The suitability of winter squash for drying purposes depended mainly on the dry matter content in the raw material. Although all the investigated cultivars can be used for producing chips, obtaining high quality porous cubes requires at least 15% of dry matter. ‘Justynka F1’ emerged as the most suitable cultivar for processing; both chips and cubes produced from its fruits were characterized by a high sensory quality and contained significant amounts of beta-carotene (225- 253 μg g-1). Also, the cultivar ‘Amazonka’ could be considered for the production of chips as it allowed us to obtain a product with a high beta-carotene content (200 μg g-1) and good sensory properties. The dried ready-to-eat crispy vegetable snacks made from the new cultivars of winter squash could be exploited as a novel attractive product with the attractive taste and colour to serve as a valuable source of carotenoids in human diet.     

Effect of storage period on physiochemical,total phenolic content and antioxidant properties of bran enriched snacks

The objective of this investigation was to compare total phenolic content and antioxidant activities of various types of cereal brans enriched snack as affected by storage conditions. Extruded snacks were prepared by the addition of cereal brans (wheat, oat and rice) singly and in combination (w:r:o::2:1.5:1.5) to rice flour at 10, 20 and 30 % bran supplementation. The content of total phenolics in the extracts (conventional and microwave assisted extraction) was determined spectrometrically according to the Folin–Ciocalteu procedure and calculated as gallic acid equivalents. Radical scavenging capacity measured by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) methods was studied. The effect of the storage on antioxidant content and capacity showed that total phenolic content and antioxidant activities of bran enriched snacks decreased during storage at ambient temperature. However, a little increase in moisture content, water activity and free fatty acid was observed in six of month’s storage period.     

Application of response surface methodology for studying the quality characteristics of cowpea-fortified nixtamalized maize

Studies were conducted on the chemical and functional properties of fermented cowpea-fortified nixtamalized maize using response surface methodology. The central composite rotatable design for K=3 was used to study the combined effect of lime concentration (0–1%), moisture content (55–65%) and cowpea level (0–30%) on pH, titratable acidity, water absorption, protein and viscosity of fermented nixtamalized maize. Regression models were developed to predict the variables. The presence of lime and cowpea influenced the pH, titratable acidity, water absorption, protein content and the cooked paste viscosity of the fermented cowpea-fortified maize. The presence of lime during fermentation generally decreased titratable acidity, water absorption and cooked paste viscosity while the addition of cowpea increased most of the studied indices. Cowpea fortification can therefore be used to increase the nutritive value of nixtamalized maize with acceptable product quality characteristics.     

Effect of moisture content on mechanical properties of rice kernels under quasi-static compressive loading

Quasi-static compressive tests to determine the static mechanical properties of individual rice kernals were carried out on specimens tested uniaxially along the longitudinal axis. Apparent elastic modulus, failure stress, failure strain and energy density at failure were determined at five or six different moisture content levels ranging from 5% to 30% on dry basis (db). Compression speeds of 5 mm min⁻¹ and 10 mm min⁻¹ were used.Statistical analysis of the test results showed that moisture content had profound influence on the properties examined, especially in the range of 12% db to 18% db where quite drastic changes occur. An explanation in terms of bound water and free water in the kernel is given.     

Physical evaluation of popped cereal snacks with spent hen meat

Various blends of spent hen meat and grains (potato starch, corn starch, and rice flour) were popped using a popping machine. Lowest bulk density was observed in the snack with 1:2 ratio of meat and potato starch. Except for the popped snack with meat and rice flour, as the starch content increased, bulk density decreased gradually. Popped snacks with grains only were higher in L* value than those with meat and grains. The a* and b* values increased with increasing meat content. All popped snacks were significantly different (P<0.001) in bulk density, color, and breaking force. As the grain content of snacks increased, the size of the air cells also increased. Results of scanning electron microscopic and optical microscopic observations revealed the popping degree of snack with starch and spent hen meat was affected by the presence of meat. The optimum ratios of meat to grain for high expansion ratio were determined to be 1:2 and 1:3 of meat to corn starch and potato starch.