Studies on Polyphenol Oxidase Activity of Heat Stabilized Whole Wheat Flour and its Chapatti Making Quality

Studies were conducted to evaluate the effect of heat treatment on polyphenol oxidase (PPO) activity of whole-wheat flour (WWF) as well as its chapatti making quality. Whole wheat flour samples were heat treated through various means such as (i) dipping in boiling water (BW) for 20, 30, 40, 50, and 60 min; (ii) inpack heating under pressure (PH) at 0.352 kg/cm² for 4, 6, 8, 10, and 12 min; (iii) microwave heat treatment (MW) at 900 Watt, 2450 MHz for 20, 40, 60, 80, and 100 s. Studies showed that the heat treatment effectively reduced PPO level in whole wheat flour; although, it had adverse effect on the dough-making quality. Based on textural analysis of dough and chapatti as well as sensory scores of chapatti, the conditions for each of the treatments were optimized, i.e., (i) Dipping in boiling water (BW) for 30 min; (ii) inpack heating under pressure (PH) at 0.352 kg/cm² for 10 min; and (iii) microwave heating (MW) for 80 s. A maximum reduction (71.2%) in PPO activity of WWF using microwave treatment could be achieved followed by PH (56.9%) and BW (38.3%). The changes in colour of unbaked chapattis (flattened circular dough, diameter 150.0 mm and thickness 2.0 mm) and changes in quality of baked chapattis were measured to assess the effectiveness of the heat treatment. The L-value (lightness) decreased from 65.2 to 55.8, 65.7 to 58.3, 65.9 to 61.4, and 64.8 to 49.1 in case of BW, PH, MW treated, and control samples, respectively during the 72 h of storage under refrigeration temperature (5–6°C).     

Effect of freeze–thaw cycles and additives on rheological and sensory properties of ready to bake frozen chapaties

The wheat grains were conditioned at 18% moisture level for 1 h followed by heating for 80 s in a microwave oven to reduce the activity of polyphenol oxidase as well as other lipolytic and oxidative enzymes. The dough samples were prepared from whole wheat flour (milled from microwave treated wheat grains) using 68% water and 2% salt on flour weight basis as common ingredients. The additives like glycerol monostearate and glycerol (5% and 1% respectively on flour weight basis) were also used in order to study their effects on the quality of ready to bake frozen chapaties (R-BFC) during freeze–thaw cycles. Alveographic properties of R-BFC as well as textural profile and sensory quality of chapaties prepared from R-BFC samples were evaluated during repeated freeze–thaw (FT) cycles. Results showed that the alveographic properties (P, L, and W) decreased significantly ( P  ≤   0.05) in all the samples after each FT cycle, while glycerol added samples showed the least changes. Chapati hardness increased in all the samples up to fourth FT cycle, thereafter sharply decreased. However, chapaties with 1% glycerol were rated better in terms of mouth feel and texture during FT cycles.     

Effect of temperature and consistency on wheat dough performance

The effects of the dough consistency (DC; 300–700 BU), temperature of mixing (16–32 °C) and temperature along fermentation (15–35 °C) on the wheat bread dough performance during mixing, proofing, cooking and cooling have been studied through a central composite experimental design. Farinograph responses revealed the significant role of DC (α < 0.001) and mixing temperature (MT) (α < 0.001) on wheat bread dough elasticity. Fermentation responses obtained from the rheofermentometer showed that the DC induces a significant positive linear effect on dough development, whereas gas development was mainly governed by the fermentation temperature. The wheat bread dough behaviour subjected to a dual mechanical shear stress and temperature constraint showed that DC had a significant linear and positive effect on the starch gelatinisation and gelling process. Therefore, breadmaking is highly governed for DC, namely dough hydration, which has a direct consequence on the mixing, fermenting, cooking and cooling performance of the wheat bread dough.     

A comparison of the functional characteristics of wheat stored as grain with wheat stored in spike form

In this study, wheat grain and wheat spike with 12%, 14% and 16% moisture content were stored at 10, 20 and 30 °C for 0, 3, 6 and 9 months. After storage, wheat samples were investigated for hectolitre weight, gluten content, Zeleny sedimentation volume, enzyme activity, acidity, phytic acid and L colour value. Storage of wheat at different storage forms (spike and grain) and storage conditions showed considerable changes in grain quality. In general, the storage period of 3 months positively affected wheat quality. However, hectolitre weight, gluten, Zeleny sedimentation, enzyme activity, acidity and colour of wheat got worse at storage periods beyond 3 months. Hectolitre weight, wet and dry gluten, Zeleny sedimentation, phytic acid content and L Colour value of wheat stored in both spike and grain form significantly decreased during storage. However, the increase in grain moisture content, storage time and temperature resulted in significant increase in total titratable acidity and falling number values of wheat. Falling Number and phytic acid values of wheat stored in spike form were generally lower than wheat stored in grain form. Storage in spike form had a positive effect on especially wet gluten content of wheat stored at non-optimal storage conditions such as high grain moisture content and high temperature. Wet gluten of wheat stored in spike form was higher than that of wheat stored grain form after storage at 30 °C for 6 and 9 months. Wheat stored in spike form is more resistant than wheat stored in grain form against adverse storage conditions such as high moisture content and temperature and longer storage time.     

Effect of heat treatment on curcuminoid, colour value and total polyphenols of fresh turmeric rhizome

Studies were undertaken to examine the effect of heat treatment on total phenolic content (TPC), colour value (yellowishness and brightness), polyphenol oxidase (PPO) activity and curcuminoid of fresh turmeric rhizome. Fresh turmeric rhizomes were subjected to heat treatment at different temperatures (60–100 °C) for different durations (10–60 min), causing a reduction in browning which was evident from the improved yellowishness and brightness. Activity of PPO was also decreased during heat treatment and PPO was almost inactivated when heated at 80 °C for 30 min. TPC of heat-treated turmeric after drying (powder) is significantly higher than that after the fresh process. TPC values increased gradually when samples were heated from 60 to 80 °C. At 90 and 100 °C, TPC values were almost identical. Maximum brightness and yellowishness were obtained when the turmeric was heated above 80 °C. Quantitation of curcuminoids in the turmeric sample was made with high performance thin layer chromatography (HPTLC). There was no significant change in the concentration of curcuminoids among the heat-treated samples. But in the sun-dried samples, a significant reduction in curcuminoid concentration was observed.     

Optimisation of baking parameters of chapati with respect to vitamin B1 and B2 retention and quality

Vitamin losses during processing of cereal grains and their food products play an important role in human vitamin intake. Therefore, experiments were conducted to optimise the baking parameters for chapati, a flat unleavened, hot-plate-baked product of Asian diet. In the experiments, whole-wheat flour (100% extraction rate) was used for the preparation of chapaties. Central composite rotatable design with three independent variables (thickness of dough sheet, time as well as temperature of baking) at five levels and nine dependent variables, i.e. vitamin B₁ and B₂ content, textural properties and overall acceptability scores, were used to conduct the experiments. The ranges for three independent variables were: thickness, 2.5–4.5 mm; time, 2.0–3.0 min; and temperature, 200–240 °C. Thickness of the dough sheet had a significant ( P  ≤ 0.05) positive effect on vitamin retention, while the temperature had greater negative effect as compared with the time of baking. Based on compromise optimisation, optimum conditions for baking of chapati, especially with respect to vitamin retention were: thickness of dough sheet 3.2 mm, time of baking 2.1 min and baking temperature 216.3 °C.     

Rennin-like milk coagulant enzyme produced by a local isolate of Mucor

Among 20 isolates of Mucor isolated from various environments in Jordan and found to produce a rennin-like acid protease, known as Mucor rennin-like enzyme (MRE), Mucor J20 was found to produce the highest level of MRE. The optimum incubation conditions for enzyme production in a fortified wheat bran mixture using solid-state fermentation were 3–4 days at 30°C. The highest MRE activity (185–200 rennin units or RU) was produced in a medium containing wheat bran and lentil straw (1 : 1 w/w) moistened with whey, and incubated in clay pots at 30°C for 4 days. A slightly lower activity value (178 RU) was found when using a mineral salt solution or distilled water instead of whey, or when using wheat bran alone with whey. At pH 4, the MRE retained its complete activity (100%) for 6 weeks at 5°C and 10°C, and for 3 and 2 weeks at 20°C and 30°C, respectively. After heating at 60°C for 10 min, the enzyme lost its activity at all pH levels used (pH 2–8). The crude extract of MRE was successfully applied in the manufacture of a cheese curd.     

Extension of shelf-life of whole-wheat flour by gamma radiation

The effect of low-dose gamma irradiation (0.25–1.00 kGy) on pre-packed whole-wheat flour (atta) was assessed in terms of physico-chemical properties, nutritional quality, chapati-making quality and sensory attributes. Semi-pilot scale storage studies on irradiated pre-packed whole-wheat flour revealed that there was no adverse effect of irradiation and storage up to 6 months of whole-wheat flour treated at doses up to 1.00 kGy on total proteins, fat, carbohydrates, vitamin B₁ and B₂ content, colour index, sedimentation value, dough properties, total bacterial and mould count. Storage of wheat flour resulted in slight increase in moisture, free fatty acids, damaged starch, reducing sugars and slight decrease in gelatinization viscosity.
However, irradiation as such had no effect on any of these parameters. Irradiation at 0.25 kGy was sufficient to extend the shelf-life of atta up to 6 months without any significant change in the nutritional, functional attributes. Chapaties made from irradiated atta (0.25 kGy) were preferred even after 6 months storage, compared with the control.     

RHEOLOGICAL AND SENSORY QUALITY OF READY-TO-BAKE CHAPATTI DURING FROZEN STORAGE

The effect of prolonged frozen storage at − 18C, on the textural and sensory properties of ready-to-bake frozen chapatti (R-BFC) was evaluated. The R-BFC samples were prepared from normal- (control) and microwave-treated (18% moisture content for 80 s) wheat grains. Results showed that the extensibility of dough and maximum load for resistance increased gradually in both the samples during frozen storage; however, the increase was lesser in the treated ones. Chapattis prepared from both R-BFC samples exhibited higher hardness, cohesiveness, chewiness and lower springiness values during frozen storage. Microwave-treated R-BFC samples were rated as better retained in color, texture and overall acceptability scores as compared with control, up to 6 months of storage at − 18C. Thiamin and riboflavin contents were monitored during frozen storage and a loss of 12.0–14.5% in thiamin and 4–6% in riboflavin after 6 months of frozen storage was recorded.

PRACTICAL APPLICATIONS

During frozen storage, various physical, rheological and sensory changes occur in the food products, which determine the consumer's acceptability. The results of this study will help to establish quality of the frozen chapattis with respect to texture, color and aroma which will meet the consumer's acceptance. The protocol for the storage of frozen chapattis will help the industry to deliver the product of optimum quality.     

Effect of moisture content, storage temperature and storage period on colour, ascorbic acid, lycopene and total flavonoids of dried tomato halves

Dried tomato halves with three storage moisture contents [18%, 24% and 30%, wet basis (wb)], packed in glass jar, plastic container and polyethylene bag were stored in room and cool-chamber environments for 5 months. During storage period average room and cool-chamber temperatures were 20 ± 4 and 5 ± 1 °C respectively. Changes of colour, ascorbic acid, lycopene, total flavonoids and moisture contents were monitored 1-month interval. Significantly higher losses of colour, ascorbic acid, lycopene and total flavonoids were found for room environment than those of cool chamber. A set of regression equations had been developed for colour, ascorbic acid, lycopene and total flavonoids as a function of storage time. No visible microorganisms were detected in the samples during the storage period. Dried tomato with ≤24% (wb) moisture content may be recommended to store in cool chamber (5 °C) and ≤18% (wb) to store in room environment (20 °C) both to be packed in glass jar.     

EFFECTS OF SOY PROTEIN AND FREEZING TREATMENTS ON COOKING LOSS AND COMPOSITION OF BEEF PATTIES

All-beef and soy-extended patties were frozen to −18°C in either 24, 48, 72 or 96h and stored at −23, −18 or −7°C for 6, 9, 12, 18 or 24 months. The addition of soy resulted in a substantial reduction in cooking loss for patties cooked from the frozen state with a greater retention of moisture in cooked patties. Freezing reduced cooking loss for soy-extended patties, but increased cooking loss for all-beef patties. Faster freezing (-18°C in 24 h vs. −18°C in 96 h) reduced cooking loss and produced higher moisture values in all-beef patties. Patties stored at –7°C lost more moisture during cooking. Increased frozen storage time had a minimal effect on cooking losses, moisture and fat levels. Where it is essential for frozen patties to sustain minimal cooking losses with maximal moisture in cooked patties, the inclusion of soy protein concentrate, faster freezing, and storage at –18°C or colder are suggested.     

微波处理对全麦粉理化性质及全麦鲜湿面品质的影响

为解决全麦粉加工品质和储藏稳定性的不足,采用微波处理全麦粉,用粉质仪和动态流变仪研究微波处理对全麦面团流变学特性的影响;用快速黏度分析仪(RVA)、X射线衍射仪、SDS-聚丙烯酰胺凝胶电泳(SDS-PAGE)等分析全麦粉中淀粉和蛋白组分结构和理化性质的变化;并验证了微波处理对全麦粉中微生物和多酚氧化酶的抑制效果和对全麦鲜湿面品质及褐变程度的影响。结果表明,微波处理可以显著提高全麦面团的稳定时间,增加面团的弹性和类固体性质,同时可改善全麦粉的黏度特性,使淀粉结晶特性略有提高;SDS-PAGE图谱显示,微波处理可引起全麦粉中蛋白组分发生有限聚合,这种聚合作用主要由二硫键引起。微波处理能够显著降低全麦粉中的菌落总数和PPO活性,抑制全麦鲜湿面褐变,提高面条煮后拉断力。     

Effect of temperature and fruit-moisture content on discolouration of dried, sulphured Bon Chretien pears during storage

Summary Discolouration of Bon Chretien pears which had been treated with sulphur dioxide and which had moisture contents of either 16, 18 or 20%, was monitored during storage at 4, 7, 10 and 20 °C. Colour was quantified in terms of CIE L*, a*, b*, hue and chroma. L* was used to predict quality retention. Discolouration was categorized as a decrease in all colour parameters, except a* which increased with storage. Measurement of L* showed that only fruit at 16% moisture content and stored at T ≤ 10 °C retained their original colour. The rate of change in overall colour was observed in the following order at 20 °C, 20% > 18 > 16% moisture content. Fruit with 18 and 20% moisture content could be stored at 10 °C for at least 140 weeks without changing their quality grading. Storage at 20 °C shortened this period to 60 and 27 weeks for fruit at 18 and 20% moisture content, respectively.     

MICROBIOLOGICAL QUALITY OF WHEAT STORED UNDER DIFFERENT CONDITIONS IN TURKEY

Four different types of wheat storage systems are widely used in the Marmara region. The existing storage conditions were studied and changes in the microbiological quality of the stored wheat under these conditions were assessed.
Depending on the external conditions, ambient temperatures and relative humidities in the stores were 17–26°C and 50–65% RH during summer and 3–10°C and 62–83% RH during winter, respectively. The low relative humidity level during harvesting and subsequent storage was adequate for obtaining low levels of moisture content and water activity in the produci for safe storage. The increase in relative humidity of the air during winter months did not affect the moisture content of the product considerably and the low temperature prevented mold growth. Therefore, all of the four different storage facilities were suitable for safe storage of grain for a period of one year without significant losses in quality due to microbiological load.     

Comparative studies of different heat treatments on quality of fried shallots and their frying oils

The objectives of this study were to compare the quality of shallot-flavoured frying oil from microwave heat treatment with that from gas heat treatment. Frying of shallot pieces by the microwave treatment required shorter heating time to obtain the same colour quality as through gas treatment. The amount of total volatile compounds of shallot-flavoured frying oil obtained from microwave treatment was greater than that from gas treatment. Oil-frying of shallots by microwave heating showed better oil quality, with lower acid and peroxide values than after frying by gas heating. In storage tests these two differently treated oils at 25°C, the acid value (AV) showed no significant increase during storage for 80 days. However, the peroxide value (PV) of these two oils increased in parallel as storage time increased. The effect of moisture content, of the shallots, on the quality of resultant shallot-flavoured frying oil was studied. Slight moisture reduction of shallot pieces from 72 to 63%, by a toasting pretreatment gave the highest amount of total volatile compounds of the shallot-flavoured frying oil. However, this total volatile compounds decreased if the moisture content of shallot pieces was less than 63%.     

Novel microwave–freeze drying of onion slices

The present study aimed to introduce the capability of a novel dehydration technique. To do so, slices with various thicknesses (3.5 and 7 mm) of white onions were dried using commercial freeze drier (abs. pressure 0.005 mbar, temp. 45 °C), our own designed microwave-vacuum drier (abs. pressure down to 300 mbar) under various microwave powers (120–1200 W) and microwave-vacuum–freeze drier (onion slices kept at −20 °C for 2 h). Then, their dehydration rates and some quality parameters, such as rehydration ratio, colour ( L*, a* and b* ) and micro-structure were investigated. Our findings showed that microwave-vacuum–freeze drier is practically a rapid, simple, efficient, economic and novel dehydration technique which can be used for dehydration of mainly foodstuffs. The quality properties of slices produced by this novel method were also completely comparable and competitive with commercial freeze drier with over 96% saving on processing time and enormous amount on energy and capital investments.     

STUDY ON INTERACTION AMONG EXTRUSION-COOKING PROCESS VARIABLES AND ENZYME ACTIVITY: EVALUATION OF EXTRUDATE STRUCTURE

A blend of wheat flour (moisture content 11.61%) and different amounts of two commercial enzymes like GRINDAMYL (GA) amylase 1000 (0–0.1 g/kg) and GA protease 41 (0–1.0 g/kg) were extruded through a co-rotating twin-screw extruder.
The effects of barrel temperature (60–120C), dough moisture (20–36%), screw speed (100–400 rpm) and different amounts of enzymes on structure of extrudates (porosity and break strength) were studied using response surface methodology.
Results showed that the highest value of porosity (62.47%  ±  4.07) was obtained at the highest value of barrel temperature (120C) and at the largest amounts of GA protease 41 (1.0 g/kg) or GA amylase 1000 (0.1 g/kg). However, the simultaneous addition of large amounts of both enzymes caused a negative effect on expansion degree (porosity  <  30%). Large amounts of moisture dough and GA amylase 1000 resulted in a high value of break strength (25.7 N/mm²) and in stiff-textured extrudates .

PRACTICAL APPLICATIONS

This research could provide some information about the effects of and the interactions between extrusion parameters and enzyme activities, which are commonly used to produce bakery products, in order to improve the texture of extrudates processed at low barrel temperatures, i.e., 60C, for example, extrudates with thermolabile components like vitamins or extrudates with high lipid fraction like breakfast cereals, pet food, etc.     

Wheat cultivars grown under organic agriculture and the bread making performance of stone-ground whole wheat flour

Stone-ground whole wheat flour is characterised by coarse bran particles and high germ content. Five wheat cultivars were grown over a 3-year period in eight organic farms in Quebec (Eastern Canada) to determine their respective effects on the quality of stone-ground whole wheat bread flour. Grain yield (1.2–3.9 t ha⁻¹), grain protein content (11.3–13.1%, based on 13.5% moisture) and dough mixing stability (6.9–11.1 min) of whole wheat flour varied much according to the farming sites. Whole wheat flour from AC Brio significantly gave the lowest pan bread volume ( P  < 0.05) and best results were obtained with Celtic (whatever the farming site) and site #5 (whatever the cultivar, probably with the exception of AC Brio). Thorough wheat cultivar selection and organic field management would be critical to get whole wheat bread with the highest specific volume.     

Quality and textural behaviour of par-baked and rebaked cake during prolonged storage

The effect of par-baking and refrigerator storage on the quality of cake was investigated. Quality evaluation of rebaked cakes was performed by using physical, chemical and instrumental texture profile analysis. Cakes were par-baked for 15, 20 and 25 min at 175 °C and then they were stored at refrigerator temperature (4 °C) for 30, 60 and 90 days, wrapped with two polyethylene bags. After storage, par-baked cakes were rebaked at 175 °C and were subjected to analysis. Par-baking and intermediate storage time had a significant effect on baking loss, crumb moisture content, colour, symmetry index and textural properties of cake. The increase in the par-baking time led to a decrease in the baking loss and an increase in the moisture content of cake. Specific volume, moisture content, L colour value and symmetry index significantly decreased with increasing intermediate storage time, while baking loss significantly increased. However, regarding the crumb hardness, cohesiveness, springiness, gumminess and chewiness, the results indicated that the best result was obtained when cakes were baked for 15 min at the par-baking stage. Overall, the cakes became firmer, less cohesive and less dry crumb as the intermediate storage time increased, whereas springiness increased.     

Comparison of seven methods for stored cereal losses to insects for their application in rural conditions

There are several methods for assessing harvest losses during storage with varying degrees of accuracy, reliability and practical application, however, field conditions may limit their use among subsistence farmers and traders in developing nations. We compared seven standard grain loss methods during natural and controlled infestation by Sitophilus oryzae L. in wheat and barley to select the best procedures for use in farm storage. Methods tested were: 1) visual inspection of infested lots, 2) uncorrected weight loss, 3) modified standard volume/weight ratio, 4) grain count and weight, 5) percentage of damaged grains converted to weight loss, 6) one thousand grain mass, and 7) one thousand grain mass including dust. Previously disinfested cereal lots (wheat, barley, 500 g fresh w) were exposed to 20 newly emerged adult S. oryzae for 90 d at 28 °C and 70% r.h. Naturally- infested wheat lots were also monitored under the same conditions. Before and after this period, fresh and dry weight, number, moisture content of uninfested and damaged grains, weight of 1 L of seeds and dust produced by insect activity, fresh and dry weight of 1000 kernels, and number of adult weevils was determined and applied to appropriate equations of methods (1), (2), (3), (4), (5), (6) and (7). Grain mass loss estimations varied by wide margins (9.3 ± 1.3% to 25.8 ± 2.3% in barley, 2.2 ± 0.7% to 12.5 ± 2.5% in wheat) depending on method employed, suggesting the need for careful selection of the most appropriate procedure under field conditions and farmer/trader interests. While accurate procedures such as method 7 provided dependable results, methods 3 and 5 appear most practical for wheat and barley.