The Use of Response Surface Methodology to Optimise Malting Conditions of Proso Millet (Panicum miliaceum L.) as a Raw Material for Gluten‐Free Foods

Response surface methodology was used to investigate the influence of the three malting parameters, i.e. degree of steeping, germination time, and temperature on the quality of proso millet malt. Each predictor variable was tested at three levels. Germination times varied from 5, 6, and 7 days, degrees of steeping were 44, 48, and 52%, and germination temperatures were 16, 20, and 24°C. A set kilning temperature of 65°C was used for all malts. A series of malt quality parameters were investigated including extract, apparent attenuation limit, gelatinisation temperature, α‐amylase activity, β‐amylase activity, limit dextrinase activity, Kolbach index, α‐amino nitrogen, viscosity, and colour. The optimal malting program was achieved after the fifth day of germination, 44% degree of steeping, and a 22°C steeping and germination temperature. The obtained values for the amylolytic and cytolytic attributes were 64.8% extract, 1.383 mPa × s viscosity, 76.0% apparent attenuation limit, 111 U/g α‐amylase activity, and 102 U/g β‐amylase activity.     

The Influences of Steeping Duration and Temperature on the α‐ and β‐Amylase Activities of Six Thai Rice Malt Cultivars (Oryza sativa L. Indica)

A preliminary study of malting conditions for six Thai rice cultivars was conducted. Three non‐glutinous rice cultivars (KDML105, PT60, and WR) and three glutinous rice cultivars (SPT, RD6, and KND) were selected. The steeping durations (24, 48, and 72 h) and temperatures (20, 25 and 30°C) were investigated for their effect on α‐ and β‐amylase, the key enzymes for malt quality evaluation. During steeping, the production of both enzymes was lower than at the germination process. The longer the steeping duration, the lower the maximum β‐amylase activity obtained. The contradictory effect was observed for α‐amylase activity, near the end of the germination time. Additionally, temperature influenced the water absorption content as well as the amylolytic enzyme activity. Particularly at 30°C, the maximum β‐amylase activity (6.7 unit/mg protein) was found in KND malt steeped for 24 h, and maximum α‐amylase activity (20 unit/mg protein) was found in PT60 malt steeped for 72 h. The amount of enzyme production depended on the variety rather than the amylose content in the rice. The optimal condition for malting rice regarding β‐amylase activity and α‐amylase activity was analyzed at 30°C, with steeping for 24 h and germination for 4–5 days.     

Control of Superoxide Dismutase Activity during Malting Using Plackett‐Burman and Box‐Behnken Experimental Design and Its Effect on Reducing Power of Wort

The Plackett‐Burman multifactorial design was employed to screen the important malting parameters for superoxide dismutase (SOD) in final malt of Ganpi‐3. The eight factors screened for SOD were steeping temperature, steeping time, peroxide hydrogen concentration in steeping water, germination temperature, germination time, withering temperature, drying temperature and kilning temperature. Variance analysis showed that steeping time, germination temperature and kilning temperature were significant for SOD activity. Box‐Behnken experimental design was further used to optimize the levels of the above three factors. By response surface methodology and canonical analysis, the optimal malting factors for higher SOD activity in final malt were: steeping time 42.2 h, germination temperature 16.9°C and kilning temperature 82.9°C. Under these conditions, the model predicted a SOD activity of 2234 U/g of dry weight malt. Verification of the optimization showed that a SOD activity of 2220 U/g was observed under optimal conditions. It showed that the experimental data could be reliably predicted by the polynomial model. Besides Ganpi‐3, three other barley varieties including Ganpi‐4, Ken‐2 and Hamelin were malted under optimal and common conditions under laboratory conditions. To some extent, SOD activities were higher in malts from the optimal malting process than those from the common malting process. Especially, SOD activities in Ganpi‐3 and Hamelin increased by 18.8% and 15.3%, respectively. Furthermore, twenty‐nine samples of malts, including eleven imported malts and eighteen domestic malts, were used. Relationships between SOD activity in malt and the reducing power of wort were examined. There was significant correlation between SOD activity and the reducing power of wort (R² = 0.8069).     

Malting of Sorghum: Further Studies on Factors influencing α‐Amylase Activity

The effects of steep regime, nature of alkaline steeping agent, and kilning condition on α‐amylase development were studied for four Nigerian sorghum cultivars. Malt α‐amylase activity was highly significantly (p<.001) influenced by all the four factors as well as their various assortments of interaction. Generally malts from the Local Red (LR) variety produced the highest a‐amylase values, followed by those of SK 5912, Local White and KSV 8 in the above sequence. The presence/absence of air‐rest processes in steep regimes was a significant factor (p<.001) influencing malt α‐amylase response to final warm steeping as well as to the other factors under study. Similarly, the nature of the steeping agent was a very significant determinant of malt α‐amylase response to kilning condition and regime of steeping. Of significant interest was the observation that Ca (OH)₂ steeps enhanced malt α‐amylase activity at the higher temperature of kilning. The significantly lower α‐amylase values given under similar conditions by the other alkaline liquors suggest a possible increase in malt thermostability due to steeping in Ca (OH)₂. Additionally, the fact that the extent of enhancement of malt α‐amylase activity by Ca (OH)₂, at 50°C Kiln temperature, was regime‐dependent, suggests that the latter was an important modulator of sorghum germination physiology.     

Effect of Malting Conditions on Pearl Millet Malt Quality

The effect of malting conditions on pearl millet malt quality in two varieties, SDMV 89004 and SDMV 91018, was investigated. Grain was steeped and germinated at four temperatures, 20°, 25°, 30° and 35°C, over 5 days. Generally, malt quality parameters (percentage of roots and shoots, diastatic power (DP), α‐ and β‐amylase activity, free α‐amino nitrogen (FAN), and malting loss) were significantly affected (P < 0.001) by germination temperature and time, as well as by variety. Malt FAN and malting loss were not affected by variety. A germination temperature of 25–30°C and germination time of 3–5 days were optimal. These conditions resulted in high DP, α‐ and β‐amylase activity, good FAN and moderate malting loss. These malting conditions and the subsequent malt quality of pearl millet are similar to those reported for sorghum. Pearl millet malt can therefore be used for the production of sorghum type beers.     

Optimization of the sorghum malting process for pito production in Ghana

Pito is an alcoholic beverage obtained through a yeast (Saccharomyces cerevisiae) fermentation of wort extracted from sorghum (Sorghum bicolor L. Moench) malt. The malting conditions of sorghum are thought to influence the quality characteristics of the malt, and subsequently the quality of the pito obtained from it. Studies were carried out on a local sorghum cultivar grown in Ghana – chireh, to optimize the conditions for malting conditions for pito production in Ghana. A 3³ full factorial experimental design was replicated with steeping times of 12, 16 and 22 h, germination times of 3, 4 and 5 days, and malt drying temperatures of 30, 40 and 50 °C as factors. Diastatic power, extract yield, attenuation limit and free amino nitrogen were determined. Germination duration significantly affected diastatic power and free amino nitrogen (p < 0.001). Extract yield was also significantly influenced by germination duration (p = 0.001). The germination time, steeping time and drying temperature had no significant effect on the attenuation limit. The optimal conditions for malting this specific cultivar grown in Ghana to obtain critical malt quality indices are 12.0–12.5 h steeping, 5 days of germination at 30 °C and drying at 40 °C. Free amino nitrogen levels in all treatments were higher than the minimum requirement for good yeast nutrition and fermentation. Copyright © 2015 The Institute of Brewing & Distilling     

Steeping‐induced physicochemical changes of milled waxy rice and their relation to the quality of yukwa (an oil‐puffed waxy rice snack)

The influence of water‐steeping periods (0 to 15 days, 25 °C) on the physicochemical properties of raw waxy rice in relation to the yukwa quality was investigated. The moisture contents in waxy rice and reducing sugar in its steeping medium were increased, while contents of protein and minerals of raw waxy rice were decreased in proportion to the water‐steeping duration. With longer steeping periods, swelling power, solubility and peak viscosity were increased, while grain hardness was decreased with apparent kernel structural change. Depending on the water‐steeping duration of raw waxy rice, the hardness decreased from 26.0 to 1.8 g, and the expansion ratio of yukwa increased from 762 to 1539%. Correlations between the physicochemical properties and yukwa quality indicated that variables having the most positive influential on expansion ratio were reducing sugar (γ = 0.961, P < 0.01) and peak viscosity (γ = 0.897, P < 0.01), and those for hardness of yukwa were crude protein (γ = 0.875, P < 0.01) and hardness (γ = 0.887, P < 0.01) of the steeped waxy rice. It is suggested that steeping‐induced physicochemical changes of raw waxy rice had a significant influence on the final quality of yukwa in terms of hardness and expansion ratio. Copyright © 2004 Society of Chemical Industry     

Physicochemical Properties of Rice Steeped in Hot or Warm Water

Prolonged steeping of rice grains in hot or warm water was examined to study the gelatinization process of rice starch. Rice treated at 75°C for 8–18 hr showed the same type “V” X-ray diffraction pattern as that of cooked rice. Rice treated at 50–60°C for 24–72 hr showed a strengthened type “A” pattern. The gelatinization degree of the 75°C treated rice determined by the β-amylase-pullulanase method and Brabender amylography was as high as that of cooked rice. The value of the 50–60°C treated rice was lower than that of raw rice. The gelatinization temperature of rice varied with the two types of treatment.     

Gel and Molecular Properties of Waxy Rice Starch

The differences in the physicochemical properties of starch (amylopectin) from waxy rices from the Philippines, Japan, and Thailand differing in processed rice quality were investigated. Samples of waxy rice starch showed final birefringence end-point temperature (BEPT) between 58 and 78°C. None of the samples showed BEPT values between 70 and 72°C. The gel viscosity values (measured with a Wells-Brookfield viscometer) of samples with BEPT values above 70°C were higher than those of samples with BEPT values below 70°C. Sedimentation coefficient and intrinsic viscosity were positively correlated and showed a U-shaped relationship with BEPT with minima at a BEPT of about 68°C. Differences in viscosity properties were mainly due to differences in the molecular weight of amylopectin, since the samples studied had similar mean chain lengths. BEPT was a useful index of amylopectin molecular weight in the waxy rice starch samples studied.     

Effects of Cooking Methods and Starch Structures on Starch Hydrolysis Rates of Rice

This study aimed to understand effects of different cooking methods, including steamed, pilaf, and traditional stir‐fried, on starch hydrolysis rates of rice. Rice grains of 3 varieties, japonica, indica, and waxy, were used for the study. Rice starch was isolated from the grain and characterized. Amylose contents of starches from japonica, indica, and waxy rice were 13.5%, 18.0%, and 0.9%, respectively. The onset gelatinization temperature of indica starch (71.6 °C) was higher than that of the japonica and waxy starch (56.0 and 56.8 °C, respectively). The difference was attributed to longer amylopectin branch chains of the indica starch. Starch hydrolysis rates and resistant starch (RS) contents of the rice varieties differed after they were cooked using different methods. Stir‐fried rice displayed the least starch hydrolysis rate followed by pilaf rice and steamed rice for each rice variety. RS contents of freshly steamed japonica, indica, and waxy rice were 0.7%, 6.6%, and 1.3%, respectively; those of rice pilaf were 12.1%, 13.2%, and 3.4%, respectively; and the stir‐fried rice displayed the largest RS contents of 15.8%, 16.6%, and 12.1%, respectively. Mechanisms of the large RS contents of the stir‐fried rice were studied. With the least starch hydrolysis rate and the largest RS content, stir‐fried rice would be a desirable way of preparing rice for food to reduce postprandial blood glucose and insulin responses and to improve colon health of humans.     

Effect of Germination Moisture and Time on Pearl Millet Malt Quality — With Respect to Its Opaque and Lager Beer Brewing Potential

The effect of germination moisture and time on pearl millet malt quality was investigated. Two pearl millet varieties SDMV 89004 and 91018 were germinated at 25°C under three different watering regimes for 5 days. As with sorghum malting, diastatic power, beta‐amylase activity, free α‐amino nitrogen (FAN), hot water extract and malting loss all increased with level of watering. However, pearl millet malt had a much higher level of beta‐amylase and higher FAN than sorghum malt and a similar level of extract. Malting losses were similar or lower than with sorghum. Thus, it appears that pearl millet malt has perhaps even better potential than sorghum malt in lager beer brewing, at least as a barley malt extender, especially in areas where these grains are cultivated and barley cannot be economically cultivated. Also, its increased use in commercial opaque beer brewing, where sorghum malt is currently used, could be beneficial.     

CHANGES IN ACTIVITY OF SORGHUM LIPASE DURING MALTING AND MASHING

Lipase activity was monitored during malting and mashing of sorghum grains. All three sorghum varieties contained detectable lipase activity in the ungerminated form. Lipase activity changed only slightly during steeping for 24 hours but increased several fold in the course of germination. Between 24% and 60% of the lipase activity of the green malt was retained after kilning at 48°C but no activity was detected in the wort after mashing at 65°C. About 68% of the lipase activity of 72 hours old malt was detected in the plumule, while 29% and 3% were detected in the endosperm and radicle, respectively. Optimum activity was observed at pH 7.0.     

Low‐ and Medium‐DE Maltodextrins From Waxy Wheat Starch: Preparation and Properties

The goal of the research was to prepare maltodextrins (MD) from waxy wheat starch and waxy corn starch (control). Waxy wheat starches with 0.2% protein, 0.2% lipid and ∼1% amylose were isolated from two flours by mixing a dough, dispersing the dough in excess water, and separating the starch and gluten from the resultant dispersion. The mean recoveries were 72% for the starches and 76% for the gluten fraction with 80% protein. Maltodextrins having low‐dextrose equivalence (DE) 1—2 and mid‐DE 9—10 were prepared by treatment of 15% slurries of waxy wheat starch and waxy corn starch at 95 °C for 5—10 min and 20—50 min, respectively, with a heat‐stable α‐amylase. Denaturing the enzyme and spray‐drying produced MD's with bulk densities of 0.3 g/cm ³. The powdery MD's were subjected to an accelerated‐rancidity development test at 60 °C, and an off‐odor was detected after 2 days storage for the low‐DE MD's from the two waxy wheat starches (WxWS₁‐MD 1.2 and WxWS₂‐MD 1.5), but not for the low‐DE waxy corn maltodextrin (WxCS‐MD 2.2) or a commercial waxy corn MD with DE 1. None of the mid‐DE 9—10 MD's developed off‐odor after 30 days storage at 60 °C. The experimental products WxWS₁‐MD 9.2, WxWS₂‐MD 9.9 and WxCS‐MD 9.1 showed high water‐solubility and gave 1—10% aqueous solutions of high clarity with no clouding upon cooling.     

黑米发芽过程中淀粉酶活力及淀粉含量变化

以黑米为原料,采用不同条件对黑米进行发芽处理,考察发芽过程中发生的生物化学变化,研究淀粉酶活力及其淀粉含量在发芽过程中的变化规律。试验证明,黑米发芽过程中的淀粉酶活力发生较大变化,呈上升趋势。淀粉含量呈下降趋势。采用Ca2+进行前处理比用去离子水进行前处理变化趋势更为显著。     

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.     

MICRO-SCALE MALTING AND BREWING STUDIES OF SOME SORGHUM VARIETIES

The malting and brewing characteristics of three sorghum varieties were investigated in a micromalting and microbrewing plant. The optimum malting conditions for Sorghum vulgare c.v. Fara Fara (Australia), Sorghum bicolor (South Africa) and Sorghum vulgare c.v. SK5912 (Nigeria) were found to consist of steeping for 21 h, at 30°C, initial germination at 30°C for 24 h, followed by a further germination period of 4 days at 25°C. Kilning temperatures of 50°C and 82°C were investigated. Evidence of the presence of hydrocyanic acid was found. The extent of modification in all malts was markedly irregular with the kernels showing brown coloration on the outer layers. The brewing trials with 100% sorghum malt showed a slow and incomplete saccharification, slow lauter tun filtrations and very difficult beer filtrations. By supplementing commercial enzymes in the mash only the speed of lauter tun filtration improved significantly.     

The Impact of Kilning on Enzymatic Activity of Buckwheat Malt

This study investigated the impact of kilning on α‐amylase, β‐amylase (total and soluble), β‐glucanase and protease activities in buckwheat malt. Common buckwheat (Fagopyrum esculentum) was steeped at 10°C for 12 h, germinated at 15°C for 4 days and kilned at 40°C for 48 h. Moisture content and enzymatic activities were determined throughout the kilning period. Results showed moisture content was reduced from 44% to 5% after 48 h of kilning at 40°C. β‐Amylase was found to exist in a soluble and latent form in buckwheat. Maximum activity of (a) α‐amylase, (b) total β‐amylase, (c) soluble β‐amylase, (d) β‐glucanase and (e) protease activity occurred after (a) 8, (b) 7, (c) 30, (d) 0, and (e) 8 h of kilning, respectively. The final malt exhibited very little β‐glucanase and cellulase activity. Proteolytic activity was low in buckwheat malt when compared to the barley malt control. All enzymatic activities were found to decrease during the kilning stage. Results indicated that after prolonged kilning at 40°C, inactivation of hydrolytic enzymes occurred; two‐stage kilning for shorter periods is recommended. Although, amylolytic activity was low in malted buckwheat, buckwheat malt shows potential as an ingredient for the brewing and cereal industry.     

Sorghum β‐Amylase Production: Relationship With Grain Cultivar,Steep Regime,Steep Liquor Composition and Kilning Temperature

Steep regime, nature of alkaline liquor, and kilning conditions were studied for their effects on sorghum malt β‐amylase development in four Nigerian sorghum cultivars. Malt β‐amylase activity was markedly (p < .001) influenced by all the four factors as well as their various interactions. Overall, malts from KSV 8 variety were the most β‐amylolytic followed in sequence by those from Local Red (LR), SK 5912, and Local white (LW) respectively. The presence or absence of air rests in steep regimes was a significant (p < .001) determinant of sorghum β‐amylase response to final warm steeping, steep liquor and kilning condition. The nature of the alkaline steep liquor was also a major determinant of the pattern of malt β‐amylase response to the kilning condition. Steeping in Ca(OH)₂ enhanced malt β‐amylase activity at the higher temperature of kilning, while KOH produced the opposite effect. Ca(OH)₂ enhancement of β‐amylase development, at a kilning temperature of 50°C, was variety‐dependent suggesting that different sorghum cultivars may employ different biosynthesis models for β‐amylase synthesis. The regime‐dependence of β‐amylase response to kiln temperature suggests that this was an important modulator of sorghum germination physiology.     

EFFECT OF GERMINATION CONDITIONS,WITH OPTIMISED STEEPING,ON SORGHUM MALT QUALITY—WITH PARTICULAR REFERENCE TO FREE AMINO NITROGEN

Using optimised steeping conditions for sorghum, the effect of various germination parameters (time, temperature and moisture) on the quality of sorghum malt for brewing purposes (in terms of diastatic power, free amino nitrogen and hot water extract) and on the associated malting losses, was investigated. Over the range studied (2, 4 and 6 days), the quality of the malt and the losses incurred during malting increased with increasing germination time. In general, the optimum germination temperature was between 25 and 30°C, and 18°C was found to be sub-optimal for the development of malt diastatic power. The quality of the finished malt and the associated malting losses were significantly correlated with the moisture content of the green malt. The root and shoot portion of the malt was found to be rich in free amino nitrogen (more than four times richer than the berry portion). Although a relatively small proportion of the total weight of the whole malt, the roots and shoots were found to contribute a substantial amount (as much as 61% under certain circumstances) to the whole-malt free amino nitrogen.     

EFFECTS OF RAISED TEMPERATURES DURING STEEPING AND GERMINATION ON PROTEOLYSIS DURING MALTING

Raising the temperature from 16°C to 20°C or 25°C for prolonged periods during steeping or germination reduces HWE and TSN and slows down wort separation in laboratory mashes. When the higher temperatures are applied only during the last steep or the first two days of germination the initial rate of modification is accelerated, as is the development of α-amylase and endopeptidase. After four or five days germination the levels of enzyme activity are substantially lower than in the control malt. However, some barleys give malts with acceptable standard analyses after 4 rather than 5 days of germination.