Survival of Aspergillus flavus conidiospores and other fungi on cowpeas during long-term storage under various environmental conditions

The survival of fungi naturally present on cowpeas (Vigna unguiculata L. Walp. ssp. unguiculata) as well as Aspergillus flavus (Link ex Fries) inoculated on cowpeas and cowpea flour was monitored over a long-term storage period. The combined effects of water activity (a_w), temperature and atmospheric gas content were evaluated. The a_w (0.66 and 0.44) did not influence survival of A. flavus at 4 and 21°C, where remarkably high viability was observed after 20 months of storage. At 37°C, loss of viability was greater than at 4 or 21°C. A more rapid reduction in the viability of conidiospores was noted at a_w 0.66 than at a_w 0.44, both on whole cowpeas and cowpea flour, when storage was at 37°C under atmospheric gas or vacuum. Total fungi (yeasts and molds) and A. flavus populations maintained highest viability when packaged under an atmosphere of nitrogen. The influence of a_w and temperature on survival of these populations was minimal in cowpeas stored under a nitrogen atmosphere.     

Cowpea cooking characteristics as affected by micronisation temperature: a study of the physicochemical and functional properties of starch

Bechuana white cowpeas were micronised to three temperatures (130, 153 and 170 °C). Cooking properties of the cowpea seeds and the role of starch‐related properties were studied. In all cases, micronisation significantly reduced the cooking time and thus the time required for the cowpea seeds to attain a suitably soft texture. This was attributed in part to the significant improvement in rate of water absorption during cooking and starch pre‐gelatinisation, as evidenced by loss of birefringence and increased susceptibility of the cowpea starch to α‐amylase digestion. However, micronisation to 170 °C resulted in a severe deterioration in pasting properties of the cowpea flour, possibly due to starch depolymerisation and/or amylose‐associated crosslinking. Owing to these changes, cowpea seeds micronised to 170 °C required a longer cooking time than the other two micronised samples. Flour prepared from cowpea seeds micronised to 170 °C may have limited starch functionality. Copyright © 2006 Society of Chemical Industry     

Cis-trans isomerisation of lycopene and colour stability of foam—mat dried tomato powder during storage

Tomato powder with ～3% moisture was obtained by foam-mat drying tomato paste (29% solids). Samples of powder were stored at various temperatures (?10° +2° +20° and +37°c), atmospheres (air, nitrogen) and humidities (with and without in-package desiccation), and colour changes were observed for periods of up to 1 year. The main cause of colour fading was the oxidation of lycopene. However, another phenomenon, trans—cis isomerisation of all-trans lycopene, can occur, with apparent loss of coloration, which is later restored by re-isomerisation. The existence of this mechanism was demonstrated by simultaneous measurements of total liposoluble colour at 420 nm and separations of carotenoid pigments by column chromatography on Al₂O₃. Neo-lycopene A (6-mono-cis-lycopene) and at least one other cis-lycopene isomer were found in fresh powder and in samples stored up to 5 months. cis-Isomers were more susceptible to oxidation. Colour changes depend upon the interplay of isomerisation and oxidation; in some cases, tomato powder was more intensively coloured after storage than when fresh. Storage at +20°c was more favourable for colour retention than storage at +2°c, or — 10°c. Excessive desiccation strongly promoted oxidation losses. Storage in an inert atmosphere improved colour retention. At +37°c non-enzymic browning, accompanied by formation of water, caused rapid darkening although carotenoid pigments were not lost to a great extent.     

Preparation and evaluation of pizza cheese made from blend of vetch–bovine milk

The objective of the study was to develop vetch–bovine milk (VBM) pizza cheese low in animal fat and its acceptability was determined through physico‐chemical, functional and sensory evaluations. Vetch (Lathyrus sativus) was detoxified by steeping in double its quantity of water for 8 h at 70 °C, changing the water seven times, draining and sun drying. Dried vetch was then treated with water at pH 4.0 at 90 °C for 60 min to deplete the beany flavour, then dried and milled into fine flour with Quadrumate Senior mill. The seed coat was separated as one of the mill fractions. Four types of VBM blends were prepared from vetch flour and bovine skimmed milk powder and were used to prepare cheese using 2.5% lactic acid bacterial culture of Streptococcus thermophillus and Streptococcus bulgaricus and rennet (0.15 mL L^?1, 1:40 ratio with water). The cheese was stored at 4 °C for 14 days and used as topping over the pizza shell. Physico‐chemical analyses, such as moisture, total solids, lactose, ash, fat, titratable acidity and pH, and sensory evaluations of both cheese and pizza were carried out at 0‐, 7‐ and 14‐day intervals. The stretchability and meltability of cheese increased significantly (P < 0.05) during storage. Commercial Mozzarella cheese was taken as a control. The results of this study suggested that VBM blend at the ratio of 12.5:87.5 (vetch flour:bovine milk powder) could be utilised to prepare a cheese of desirable characteristics for pizza topping.     

The stability of wheat starch lipids in untreated and chlorine-treated cake flours

Untreated flour and flour treated with chlorine (2.2 g Cl₂ kg_-1) were stored in air at 25°C for 4 months. Starch samples prepared from the original flours were stored in air at 25°C for 4 months. Starch samples were also prepared from the fresh flours (control starches) and from the stored flours. Some of the starches from the stored flours were subsequently held at 70°C for 1 month. Starch lipids were not affected by flour chlorine treatment, or by storage at 25°C. There was slight hydrolysis of starch lysophospholipids at 70°C, but negligible autoxidation of unsaturated fatty acids in the total starch lipids. There was appreciable hydrolysis of non-starch lipids in the untreated stored flour, but no detectable autoxidation of unsaturated fatty acids. Chlorine treatment of flour caused an immediate loss of approximately half of the oleic, linoleic and linolenic acids in all the non-starch lipids which were examined. There was no further change in the fatty acid composition of the non-starch lipids when the treated flour was stored, but lipid hydrolysis was substantially reduced compared with the untreated stored flour.     

Thiamin, Riboflavin and Niacin Retention in Cooked Cowpeas as Affected by Kanwa Treatment

Retention of three water soluble B-vitamins in dry cowpeas cooked with a local tenderizer, named “kanwa,” were investigated. Results showed cooking (100°C) in kanwa or sodium bicarbonate decreased levels and retention of vitamins compared to controls cooked in water. Levels of vitamins in kanwa-cooked cowpeas were not significantly different from those in NaHCO₃ cooked samples. Retention in the alkaline cooking processes ranged 15–20% (thiamin), 26–49% (niacin) & 53–64% (riboflavin). Soaking followed by boiling at 100°C or pressure cooking (121°C) increased levels and retention of vitamins.     

Dehulling characteristics,sensory and functional properties of flours from selected cowpea varieties

BACKGROUND: The knowledge of dehulling characteristics is very important in the selection of cowpeas for flour production. In this study the sensory and functional properties of cowpea flour as influenced by dehulling method (wet and dry/mechanical dehulling) and cowpea variety (white, maroon and mottled) were investigated. RESULTS: White cowpea showed a significantly different (P < 0.05) and higher dehulling rate (DR > 97%) for all dehulling methods. Maroon and mottled cowpeas were poorly dehulled (DR < 10%) when using the wet method (WD). Dry dehulling (DD) was effective on all three varieties (DR > 94%). The highest yield of flour was observed with white cowpea (80% for DD and 96% for WD). The beany odour intensity of flours was dependent on the method of dehulling used. Flour functionality was more significantly influenced by cowpea variety than by dehulling method. CONCLUSION: Dry dehulling could be recommended for cowpea flour production, as this method was found to be more effective on the selected cowpea varieties. Owing to the observed variation in flour functionality among cowpea varieties, the choice of a particular variety for flour production will depend on the intended use of the flour. Copyright © 2009 Society of Chemical Industry     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.     

Effects of Pretreatment on Functional and Nutritional Properties of Cowpea Meal

The efficiency of decorticating cowpeas was improved by hydrating to 25%, then drying to ?10% moisture. Effects of drying temperature (50°, 70°, 90°, 110°, and 130°C) on functional and nutritional properties of cowpea meal were assessed. Extraction rate (yield) was unaffected by heating. Average particle size and water absorption of meal were greatest for intermediate temperatures. Starch was not gelatinized at any temperature. Reduction in protein solubility, which occurred at temperature 90°C., was associated with changes in gel electrophoresis patterns. Protein solubility was negatively correlated with previously reported values for specific gravity and apparent viscosity of cowpea pastes. Increases in drying temperature reduced thiamin content and increased browning of the meal.     

The effect of rice flour on pasting and particle size distribution of green gram (Phaseolus radiata, L. Wilczek) dried batter

The effect on the pasting characteristics of green gram flour of the addition of rice flour was studied. The gelatinization temperature decreased from 75 °C for the control to 72 °C for samples containing different levels of rice flours. Average particle size of dried batter mix increased with the addition of varying percentages of rice (10, 15, 20 and 25%) from a control value of 236 μm to a maximum 310 μm. The addition of rice flour to green gram increased the water absorption in line with the amount of rice flour added. When rice flour was added, the protein content of the mixed sample of green gram batter and rice flour was reduced accordingly and the fat absorption in the samples also decreased. The foaming capacity of native ground flour, measured after 0.5 min, was double (130 mL) that of dried green gram batter (60 mL) which had been prepared by soaking, wet grinding and drying.     

Physico- Chemical Characteristics and Functional Properties of Starch and Dietary Fibre in Grass Pea Seeds

Physico-chemical and functional properties of starch and fibre in raw and processed grass pea seeds were evaluated. Whole grass pea seeds were found to contain 41 % starch and 17% total dietary fibre (2% soluble and 15% insoluble) on dry matter basis. Examination by using scanning electron microscopy revealed oval shaped starch granules with an average width of 17 μm and length of 25 μm. Raw sample had a gelatinization onset temperature of 62°C and two endothermic transition peaks at about 73°C and 94°C, in addition the starch isolated from grass pea flour was shown to have a transition enthalpy (ΔH) of 10 Jg⁻¹. The viscosity of the raw sample (using a Brabender amylograph) reached peak maximum at 80–95°C, decreasing during the 30 min holding time (at 95°C) followed by an increase during cooling to 50°C. Raw whole seed flour was shown to have a water absorption and water solubility index (WSI) of 3 and 16%, respectively. Samples that had been cooked for 60 min had a lower WSI than those cooked for 30 min; this was further reduced in the samples cooked after soaking. The carbohydrate extracted from raw flour was found to be mainly high Mwt carbohydrate (55%), eluted at Kav < 0.2.     

Effect of microwave vacuum drying and hot air drying on the physicochemical properties of durian flour

Unripe durian cv. Monthong was subjected to microwave vacuum drying (MVD) at 1200, 1600 and 2200 W and hot air drying (HAD) at 40, 50 and 60 °C to produce durian flour. Drying rate of MVD and HAD was 0.34–0.58 kg water kg dry solid^?1 min^?1 and 0.02–0.06 kg water kg dry solid^?1 min^?1, respectively. An increase in drying rate by either increasing hot air temperature or increasing microwave power decreased the degree of crystallinity from 21.95% to 2.31% and from 7.72% to 4.05%, respectively. Moreover, the increased drying rate caused a decrease in endothermic enthalpy (ΔH_gel) and pasting properties. Starch content of the durian flour was 41.40–47.03%. The starch granule morphology of durian flour was disrupted which indicated gelatinisation of flour during drying. Due to a short drying process, the MVD flour had less a*‐value (P ≤ 0.05) than the HAD flour.     

Effects of hydrothermal processing on rutin retention and physicochemical properties of Tartary buckwheat enriched dough and Chinese steamed bread

Effects of hydrothermal processing on content changes of rutin, quercetin and total flavonoids and physicochemical properties of Tartary buckwheat (TB) enriched dough and Chinese steamed bread (CSB) were investigated. Rutin loss and bitterness in CSB made from mixed wheat flour and hydrothermally processed TB flour decreased markedly compared with control. Total flavonoids were increased in dough after fermentation but decreased afterwards in CSB significantly (P < 0.05). The development time, stability time, extensibility, storage and loss moduli and tan δ of TB enriched dough, along with the volume, textural properties, sensory evaluation and bitterness of derived CSB, were significantly affected by hydrothermal processing temperature and time. Hydrothermal processing of TB flour at 100 °C for 20 min, compared with 100 °C for 10 min, 30 min or 121 °C for 10 min, 20 min, 30 min, was suggested to be a relatively better pretreatment condition for the present TB enriched CSB.     

Functionality Enhancement of Composite Cassava Flour in the Production of Maize Tuwo (A Non-fermented Maize-Based Food Dumpling)

The study was focused on the evaluation of textural and sensory quality enhancing functionality of cassava flour in the production of maize tuwo (a non-fermented maize-based food dumpling). The cassava flour was added to maize flour at the level of 5%, 10%, 15%, 20%, 25% and 30% (w/w), respectively. The bulk density and water holding capacity of maize/cassava flour mixes ranged from 0.77–0.83 g/cm³ and 1.91–2.05 g/g, respectively, while those of 100% maize flour were 0.84 g/cm³ and 2.09 g/g, respectively. There were variations in the pasting properties of maize/cassava flour mixes including the pasting temperature (75.4–78.8°C), peak viscosity (112.1–170.0 RVU), breakdown viscosity (38.4–53.7 RVU) and final viscosity (132.1–142.2 RVU), while those of 100% maize flour were 74.6°C, 108.1 RVU, 38.1 RVU and 148.3 RVU, respectively. The colour characteristics of tuwo prepared from maize/cassava flour mixes showed an increase in the colour lightness, L*-value (68.6–71.8) and chroma, C-value (9.4–11.4) while tuwo from 100% maize flour gave 67.7 and 9.1, respectively. The cohesiveness indexes (15.4–24.2%) of tuwo from maize/cassava flour mixes increased with an increase in the quantity of cassava flour in the mix while that from 100% maize flour was 15.2%. The softness indexes (17.5–18.4°mm) of tuwo from the mixes were also higher than that from 100% maize flour (17.4°mm). The sensory quality rating of tuwo from maize/cassava flour mixes showed that tuwo from 25% cassava flour inclusion was the highest in terms of texture (hand-mouldability), taste and overall acceptability while that from 30% cassava flour inclusion was the highest in terms of colour.     

Osmotic Concentration of Green Beans Prior to Freezing

Osmotic dehydration as an intermediate step in freezing of vegetable tissue was studied. Green beans c.v. Bush Blue Lake-47 were osmotically concentrated in NaCl-water solutions at three concentrations (5, 10, and 17% NaCl by weight) and three temperatures (8, 20, and 40°C). Movement of salt and water was modeled for water loss from and salt uptake by the product. Green beans contacted with 10% NaCl-water solution at 20°C for 30 min were processed further by freezing in an air blast freezer. Evaluation of color, hardness, texture, taste and overall acceptability indicated the product was organoleptically acceptable.     

Effect of extrusion conditions on the physicochemical properties of a snack made from purple rice (Hom Nil) and soybean flour blend

Soy flour was added at levels of 5%, 10%, and 15% of Hom Nil rice flour for extrusion at 190 °C barrel temperature and 350 rpm screw speed. The extruded snack qualities decreased inversely with soy flour. However, product qualities were considered to be optimised when soy flour at 5% was added. The effect of feed moisture content (15, 17, 19 g (100 g)^?1 wb), barrel temperature (150, 170, 190 °C) and screw speed (350, 400, 450 rpm) on physicochemical properties of the snack were then investigated. The physicochemical properties of the product including expansion ratio, density, water absorption index (WAI), water solubility index (WSI) and hardness were evaluated. All properties were related, as linear equations, in terms of feed moisture content, barrel temperature, screw speed with relative correlation (R²) at 0.83–0.94. The snack properties along with consumer acceptance were all highest when the extruded condition were 15 g (100 g)^?1 wb feed moisture content, 170 °C of barrel temperature and 450 rpm of screw speed.     

Thermal Processing of Cowpea Slurries

Isochronal temperature profiles of 20% cowpea flour slurries showed conduction heating while the estimated Rayleigh numbers predicted natural convection heating; apparently, the flour particles suppressed convection. Magnitudes of f_h of cowpea gels increased linearly with fat content, decreased with moisture content, and were independent of the cowpea flour particle size. The heating curve of a 10% cowpea flour slurry at 121°C showed one break due to gelation of protein and starch at about 66°C and another due to loss of rigidity at about 87°C.     

Inactivation of soya bean trypsin inhibitors by thiols

Systematic studies of factors that inactivate soya bean trypsin inhibitors showed that thiols facilitate heat inactivation, as illustrated by the following examples. Heating soya flour in an aqueous medium in a water-bath from 25 to 93°C for 1 h showed that heat alone does not begin to inactivate the inhibitor until about 55°C (around 10% inactivation). The corresponding value at 85 °C is 60%. In contrast, inactivation in the presence of N-acetylcysteine proceeds more rapidly, as shown by 70% inactivation at 55 °C and 94% at 85 °C. These results, and additional data, illustrate the complementary co-operative effect of heat and thiols in inactivating soya bean trypsin inhibitors in commercial soya flour. The thiol treatment also strikingly enhances the in-vitro digestibility of soya proteins by trypsin. The results are discussed with reference to the role of disulphide bonds in the mechanism of enzyme inhibition.     

基于表面诱捕装置的不同食料引诱嗜卷书虱效果比较研究

及时检查监测常见微小害虫书虱的发生动态有利于其早防早治和避免危害，谷物食料诱捕害虫具有取材方便、有利于提高诱捕效率以及对书虱类害虫的种群控制。在20、24和28℃温度下，研究了粮堆表面波纹板诱捕器内置小麦粉、玉米粉、稻谷粉、酵母粉、发霉小麦粉、发霉玉米粉以及发霉稻谷粉等食料后不同时间引诱嗜卷书虱Liposcelis bostrychophila的数量动态。温度28℃时，实验食料中引诱效果最好的酵母粉在14 d内可引诱嗜卷书虱数量达827头，同时发霉小麦粉、发霉玉米粉和发霉稻谷粉中引诱嗜卷书虱的数量分别达662、605和604头，未霉变小麦粉、玉米粉和稻谷粉引诱嗜卷书虱数量分别为479、460和451头。20℃和24℃温度下，以上不同食料同时引诱嗜卷书虱的数量随温度降低相应减少，如酵母粉在对应温度下引诱嗜卷书虱的数量分别降至450和628头。采用GC-MS法测定出小麦粉、玉米粉、稻谷粉、酵母粉、发霉小麦粉、发霉玉米粉以及发霉稻谷粉的挥发物种类数量分别为17、24、20、20、20、23和25种，引诱效果最好的酵母粉的挥发物中芳樟醇、异戊醇、2-甲基丁酸乙酯以及正己醇相对含量较高，同样谷物粉发霉后引诱效果显著增加且这几种挥发物含量也明显增加，初步分析桧烯、1-辛烯-3-醇、2-戊基呋喃、肉桂醛等一定量的存在可能与较好的引诱效果有关，它们对嗜卷书虱的引诱作用值得进一步关注和研究。     

Application of Enzymes in Soy Milk Production to Improve Yield

Soy milk was produced from full fat flour by preparing a slurry in water at a water to flour ratio of 10 to 1. The slurry was heated to 50°C, and different enzymes were evaluated in order to optimize protein and solids yields in the milk. The reaction period was 1 hr and after inactivation of the enzymes by boiling for 15 min the mixtures were centrifuged at 1500 ×g and the protein and dry matter solubility indices (PSI and DSI) were calculated together with protein and dry matter yields in the obtained milk. The best results were obtained with a neutral proteinase, increasing the protein and solids yields from 33% and 42%, respectively, to 73% and 66%, respectively, at 0.5% dosage level compared to the control sample with no enzyme treatment.