Off-flavor Production Research Articles

The Microbial Diversity of Sherry Wines

The principal role of wine yeast is to transform efficiently the grape-berries’ sugars to ethanol, carbon dioxide, and other metabolites, without the production of off-flavors. Wine yeast strains are able to ferment musts, while other commercial or laboratory strains fail to do so. The genetic differences that characterize wine yeast strains in contrast to the biological ageing of the veil-forming yeasts in Sherry wines are poorly understood. Saccharomyces cerevisiae strains frequently exhibit rather specific phenotypic features needed for adaptation to a special environment, like fortified wines with ethanol up to 15% (v/v), known as Sherry wines. Factors that affect the correct development of the veil of flor during ageing are also reviewed, along with the related aspects of wine composition, biofilm formation processes, and yeast autolysis. This review highlights the importance of yeast ecology and yeast metabolic reactions in determining Sherry wine quality and the wealth of untapped indigenous microorganisms co-existing with the veil-forming yeast strains. It covers the complexity of the veil forming wine yeasts’ genetic features, and the genetic techniques often used in strain selection and monitoring during fermentation or biological ageing. Finally, the outlook for new insights to protect and to maintain the microbiota of the Sherry wines will be discussed.

Rapid Screening Method for Phenolic Off-Flavor (POF) Production in Yeast

Because of an increased interest in complex niche products and the ongoing quest for improved brewing efficiency and quality, the interest in novel yeasts is increasing. However, many of these nonconventional yeasts and newly developed hybrids often produce undesirable off-flavors and, in particular, are characterized by strong production of phenolic aromas such as 4-vinyl guaiacol (4VG). Here, we describe a novel high-throughput, low-cost absorbance-based screening method that allows quick determination of the phenolic off-flavor (POF) production capacity of yeasts. We show that this method correlates well with the standard, more laborious GC-based methods and that it can be used to assess POF production of many different strains in parallel with minimal hands-on labor. This new method therefore opens exciting new routes to select rare variants or mutations that combine desirable phenotypes without showing unwanted production of POFs such as 4VG.

Chemical, physical and sensorial characterization of fresh quinoa sprouts ( Chenopodium quinoa Willd.) and effects of modified atmosphere packaging on quality during cold storage

Abstract The aim of this study was the quality characterization and the evaluation of the storage potential of “Real” and ‘Regalona Baer’ quinoa sprouts. Sprouting characteristics, texture, sensorial and chemical proprieties were evaluated on sprouts after 4 days of imbibitions and during storage in a passive modified atmosphere packaging (MAP). ‘Regalona Baer’ showed higher germination and weight increase, higher phenolic content and sensorial properties than ‘Real’. ‘Real’ sprouts also showed the shortest shelf life, whereas ‘Regalona Baer’ sprouts were still marketable after 7 days. A separate experiment was performed to study the effects of passive and active MAP with 5% O₂ + 20% CO₂ on the ‘Regalona Baer’ variety. Sprouts stored in active MAP showed a better texture and a minor production of off-flavor, compared to samples stored in passive MAP, thus showing for the first time that active packaging with 5% O₂ + 20% CO₂ may be a potential solution for allowing the distribution of this product.

Effect of modified atmosphere packaging and temperature abuse on flavor related volatile compounds of rocket leaves (Diplotaxis tenuifolia L.).

The effect of storage conditions on flavor-related volatile composition of wild rocket (Diplotaxis tenuifolia) was investigated on Modified Atmosphere packed (MAP) leaves stored under isothermal and non-isothermal conditions. In a first experiment the effect of MAP was compared to the storage in air at 5°C; a second experiment aimed to study the effect of non isothermal conditions, with two temperature abuses (at 13°C for 24h) during a 5°C. Twenty-four volatiles were detected, including C6, C5, isothiocyanate, lipid-derived and sulfur compounds. In the first experiment, MAP-stored rocket showed a slower loss of typical flavour volatiles (thiocyanates and isothiocyanates) and a slower production of off-flavors until 6days of storage, compared to leaves stored in air. After this time, dimethyl sulfide and acetaldehyde dramatically increased in MAP-stored rocket samples. In the second experiment, samples stored under non-isothermal conditions showed lower O2 and higher CO2 concentrations than samples stored under isothermal conditions. Rocket leaves stored under non-isothermal conditions showed an increased production of volatiles responsible of off-flavors (acetaldehyde and dimethyl sulfide) following temperature abuse comparing to storage in isothermal condition. Thus, dimethyl sulfide and acetaldehyde could be effective markers for tracking the effect of temperature fluctuations on rocket during storage.

Fermentation assays reveal differences in sugar and (off-) flavor metabolism across different Brettanomyces bruxellensis strains.

Brettanomyces (Dekkera) bruxellensis is an ascomycetous yeast of major importance in the food, beverage and biofuel industry. It has been isolated from various man-made ecological niches that are typically characterized by harsh environmental conditions such as wine, beer, soft drink, etc. Recent comparative genomics studies revealed an immense intraspecific diversity, but it is still unclear whether this genetic diversity also leads to systematic differences in fermentation performance and (off-)flavor production, and to what extent strains have evolved to match their ecological niche. Here, we present an evaluation of the fermentation properties of eight genetically diverse B. bruxellensis strains originating from beer, wine and soft drinks. We show that sugar consumption and aroma production during fermentation are determined by both the yeast strain and composition of the medium. Furthermore, our results indicate a strong niche adaptation of B. bruxellensis, most clearly for wine strains. For example, only strains originally isolated from wine were able to thrive well and produce the typical Brettanomyces-related phenolic off-flavors 4-ethylguaiacol and 4-ethylphenol when inoculated in red wine. Sulfite tolerance was found as a key factor explaining the observed differences in fermentation performance and off-flavor production. Sequence analysis of genes related to phenolic off-flavor production, however, revealed only marginal differences between the isolates tested, especially at the amino acid level. Altogether, our study provides novel insights in the Brettanomyces metabolism of flavor production, and is highly relevant for both the wine and beer industry.

Organic acids produced by lactic acid bacteria (Leuconostocsp.) contribute to sensorial quality loss in modified-atmosphere-packed fresh-cut iceberg lettuce

The shelf-life of fresh-cut lettuce packed in a modified atmosphere (MA) is determined by its overall visual (OVQ), being a measure of its general appearance based on colour and shape criteria. In addition to the OVQ, the development of off-flavour and acid off-smell reduces consumer acceptance of such products. Concomitant with these changes in organoleptic properties, there is a rapidly developing microbial population inside the MA package (MAP), dominated by lactic acid bacteria. We studied the bacterial population dynamics of active MAP freshcut lettuce as well as the effect of metabolites produced by the bacteria (lactic acid and acetic acid) on lettuce quality aspects. Within 3 days of packaging, the oxygen concentration in the package was reduced to near zero, and this resulted in the selective advantage of lactic acid bacteria, in particular Leuconostoc and Lactococcus species. Leuconostoc, when cultivated on lettuce-enriched artificial medium, was found to produce both acetic and lactic acids. Low concentrations of acetic and lactic acids were found in MAP lettuce after 5 days of storage at 7°C. Freshly prepared fresh-cut product treated with comparably small amounts of acetic and lactic acids showed severe quality loss. This was reflected by rapid browning, yellowing and loss of texture. The experiments demonstrate that, under anaerobic conditions, organic acids are produced by lactic acid bacteria, affecting both off-flavour production and sensorial quality in fresh-cut lettuce. © 2016, International Society for Horticultural Science. All rights reserved.

Influence of yeast strain, priming solution and temperature on beer bottle conditioning.

Recently, there has been a significant increase in the number of microbreweries. Usually, craft beers are bottle conditioned; however, few studies have investigated beer refermentation. One of the objectives of this study was to evaluate the impacts of different experimental conditions, specifically yeast strain, priming solution and temperature, on the standard quality attributes, the volatile compounds and the sensory profile of the bottle-conditioned beer. The other aim was to monitor the evolution of volatile compounds and amino acids consumption throughout the refermentation process to check if it is possible to reduce the time necessary for bottle conditioning. The results indicate that the volatile profile was mainly influenced by the strain of yeast, and this may have obscured the possible impacts of the other parameters. Our results also confirm that the two yeast strains showed different metabolic activity, particularly with respect to esters production. Moreover, we found the Safbrew S-33® strain when primed with Siromix® and refermented at 30 °C yielded the fastest formation of higher alcohols while maintaining low production of off-flavours. These results suggest a formulation that may reduce the time needed for bottle conditioning without affecting the quality of the final beer which may simultaneously improve efficiency and economic profits. © 2016 Society of Chemical Industry.

Eutrophication mediates a common off-flavor compound, 2-methylisoborneol, in a drinking water reservoir

Off-flavors, such as 2-methylisoborneol (MIB) and geosmin, cause drinking water to have earthy or musty tastes and odors. Humans can detect such compounds at minute concentrations (10 and 30 ng/L for MIB and geosmin, respectively), and, although not a health risk, off-flavors can promote consumer distrust. Removal of these compounds is costly and often unreliable or only suitable under certain conditions. Minimizing off-flavor production at the watershed-scale may be more cost-effective in addition to improving ecosystem health and aesthetics. Cyanobacteria are considered to be the primary drivers of off-flavors in freshwater systems. Due to their ability to produce toxins, cyanobacteria have been under particular scrutiny, and environmental factors promoting cyanobacterial blooms are relatively well-studied. Using this body of literature, we conducted a seven-week, limnocorral experiment where we manipulated nitrogen and nitrogen-to-phosphorus concentrations to influence phytoplankton community structure and off-flavor production. The addition of a single nutrient across broad ranges (nitrogen or phosphorus) had no effect on MIB. However, the addition of both nitrogen and phosphorus promoted high concentrations of MIB relative to treatments that received no nutrients (448% increase) or only nitrogen or phosphorus (722% increase). Interestingly, cyanobacteria waned during the experiment and were replaced by diatoms, which were the dominant taxa by the end of the experiment. Our findings clearly show that eutrophication affects MIB production, but mechanisms leading to the production of this compound may differ from what has been previously predicted.

The use of chitooligosaccharide in beer brewing for protection against beer-spoilage bacteria and its influence on beer performance.

To identify a biological preservative that can protect beer from microbial contamination, which often results in the production of turbidity and off-flavor. The antimicrobial activity of a chitooligosaccharide against beer-spoilage bacteria and its effect on the fermentation performance of brewer's yeast was studied. Chitooligosaccharide with an average 2 kDa molecular weight was the best at inhibiting all tested beer-spoilage bacteria. The application of chitooligosaccharide in the brewing process did not influence the fermentation of brewer's yeast. The change in beer performance induced by the contamination of Lactobacillus brevis could be effectively controlled by application of chitooligosaccharide in the beer brewing process. The experimental data suggested that chitooligosaccharide should be an excellent preservative to inhibit beer-spoilage bacteria in the brewing process and in the end product.

Spoilage of vacuum-packed beef by the yeast Kazachstania psychrophila

A survey of the psychrotolerant yeast microbiota of vacuum-packed beef was conducted between 2010 and 2012. Chilled vacuum-packed beef (n = 50) sampled from 15 different producers was found to have a mean psychrotolerant yeast count of 3.76 log cfu per cm2. During this assessment, a recently described yeast named Kazachstania psychrophila was shown to be associated with this product. In order to gain basic knowledge about the spoilage potential of K. psychrophila in vacuum-packed beef, challenge studies were performed and the survival of three different K. psychrophila strains was analyzed during storage of artificially contaminated beef. Beef samples were inoculated with the yeasts at a contamination level of 2 log cfu per cm2. Survival and growth of K. psychrophila strains was monitored on malt extract agar at regular intervals over 84 days. Kazachstania levels rapidly increased about 5 log units within 16 days under chill conditions (4 °C). Gas bubbles were observed after 16 days, while discoloration and production of off-flavors became evident after 42 days in inoculated samples. This study demonstrates for the first time, that the psychrotolerant yeast K. psychrophila is a dominant spoilage microorganism of vacuum-packed beef products stored at low temperatures, causing sensory defects which result in reduced shelf life, and consequently in considerable economic losses.

Early fermentation volatile metabolite profile of non-Saccharomyces yeasts in red and white grape must: A targeted approach

Saccharomyces cerevisiae is the main driver of alcoholic fermentation. It is typically inoculated at high levels to ensure successful implantation as well as reduce the risks of stuck fermentations and off-flavor production. However, winemakers have found that wines produced with only S. cerevisiae can be lacking in complexity compared to fermentations where non-Saccharomyces yeasts are more active. This study sought to understand the early fermentation characteristics of Kazachstania gamospora, Lachancea thermotolerans, Metschnikowia pulcherrima, Torulaspora delbrueckii and Zygosaccharomyces kombuchaensis in both Sauvignon blanc and Syrah musts. S. cerevisiae was used as a control. Solid-phase microextraction coupled to GC–MS was used to evaluate the musts once they reached 2% ethanol concentration. The method targeted 90 different compounds known to occur in wine and/or be produced by yeast during fermentation. For the first time, K. gamospora and Z. kombuchaensis have been studied in the context of wine. While the other yeasts are commercially available starter cultures, they have never been profiled this extensively. Analysis showed that each yeast profile was unique and different based on the must. The non-Saccharomyces yeasts produced lower concentrations of esters, alcohols and terpenes with the exception of K. gamospora which produced more total esters than the control.

Ultrasonic inactivation of microorganisms: A compromise between lethal capacity and sensory quality of milk

The aim of this study was to evaluate eight ultrasound (US) different combinations of amplitude (70 and 100%) and duration (50, 100, 200 and 300 s) for their lethal capacity against Escherichia coli, Pseudomonas fluorescens, Staphylococcus aureus and Debaryomyces hansenii, the generation of volatile compounds (VC) and their impact on milk sensorial descriptors. The strongest treatment (100% × 300 s) led to a population reduction of 4.61, 2.75, 2.09 and 0.55 log for D. hansenii, P. fluorescens, E. coli and S. aureus, respectively, but caused milk sensorial deterioration. Four descriptors (metallic, burnt, rubbery and sharp) were correlated with treatment duration. Each of them, using stepwise regression analysis, was found to be associated with one VC (dodecanoic acid, R2 = 0.90; octanoic acid, R2 = 0.82; δ-dodecalactone, R2 = 0.81 and decanoic acid methyl ester, R2 = 0.78) that could be considered as a marker for milk sensorial deterioration caused by US. In this study it is stated in what conditions ultrasounds (US) could be used as effective sanitation procedure without the production of off-flavours and what is the inactivation capacity toward E. coli, P. fluorescens and D. hansenii in that conditions. Moreover, our results indicate possible markers of milk sensory degradation caused by US treatments. These markers (dodecanoic acid, octanoic acid, δ-dodecalactone and decanoic acid methyl ester) could be used to check milk sensory quality after US treatment instead of using expensive and time consuming sensory tests.

Chilling-Induced Changes in Aroma Volatile Profiles in Tomato.

Fruit and vegetables are regularly stored by consumers in the refrigerator at temperatures that may be well below the recommended storage temperatures. Apart from causing visible symptoms such as watery, sunken areas on the skin, chilling may also induce changes in fruit textural properties and flavour. The aim of this research was to investigate the effect of low temperature storage on tomato flavour and off-flavour production. To more closely mimic the real-consumer aroma perception while eating, in addition to the standard solid-phase microextraction gas chromatography–mass spectrometry (SPME/GC-MS) analysis, volatiles were also measured using a chewing device connected to a proton-transfer reaction–mass spectrometer (PTR-MS). Aroma volatiles were assessed in red ripe tomatoes of the cvs Cappricia RZ (round truss) and Amoroso RZ (cocktail truss) stored at refrigerator temperature (4 °C) and at higher temperatures (16 and 22 °C) for 20 days. The changes in aroma production were also monitored when the fruit was brought from room to refrigerator temperature and vice versa. After bringing the fruit from room to refrigerator temperature, the abundance of most volatiles was greatly reduced within 3 to 5 h, closely following the decrease in fruit temperature. When temperature was restored to room temperature following varying times of cold storage, the abundance of most volatiles increased again, but generally not to the original levels. Overall, the effects of low temperature storage on the decrease in volatile abundance were more pronounced in cv Cappricia RZ than in cv Amoroso RZ. On the contrary, the production of off flavours following prolonged cold storage was more pronounced in cv Amoroso RZ than in cv Cappricia RZ. Apart from changes in the overall abundance of the volatiles, marked changes in the volatile profile were observed in fruit stored for longer times in the cold and this may at least in part explain the negative effect of cold storage on overall tomato flavour.

Comparison of the behaviour of Brettanomyces bruxellensis strain LAMAP L2480 growing in authentic and synthetic wines.

Brettanomyces bruxellensis is the main microorganism responsible for the production of off-flavours in wine. Studies have been carried out in synthetic cultures using p-coumaric acid for the production of vinyl and ethylphenols. The results obtained have been extrapolated to authentic wine, but there is no evidence that this correlation will be correct. We studied the behaviour of B. bruxellensis native strain LAMAP L2480 in authentic wine and in a synthetic medium with a chemical composition similar to the authentic wine used in this study (basal synthetic wine + pH, ethanol and hydroxycinnamic acid concentrations of commercial wine). In some assays, B. bruxellensis has been studied using media containing 100 mg L(-1) p-coumaric acid, so we also used the same concentration added to the authentic and synthetic wines. The microorganism showed better growth in authentic wine, regardless of the presence of p-coumaric acid. In the case of synthetic wine, the addition of p-coumaric acid caused a delay in yeast growth and an increase in the production of volatile phenols. The coumarate decarboxylase activity did not show any difference regardless of the media and the presence of p-coumaric acid. Vinylphenol reductase showed higher activity when a higher concentration of p-coumaric acid was added in synthetic wine, but no change was observed in authentic wine.

Application of Electronic Nose in Tandem with Chemometric Analysis for Detection of Alicyclobacillus acidoterrestris-Spawned Spoilage in Apple Juice Beverage

Apple juice beverage spoilage spawned by Alicyclobacillus acidoterrestris can cause sensory defect by production of medicinal off-flavor, which could hardly be noticed in the early stage and would lead to the consumer complaints and, consequently, the economic and image loss of the manufacturers. Thus, it is necessary to detect the contamination at early stage in case of serious converse effect. The aim of this study was to evaluate the performance of an electronic nose (e-nose) in tandem with chemometric analysis as online, rapid screening technique for detection of the spoilage in apple juice beverage, using test panel evaluation as reference, as well as to predict the spoilage status of apple juice beverage based on the response to the specific volatiles in it. Coupled to linear discriminant analysis (LDA), e-nose could discern the contaminated beverage after 4 h, corresponding to the bacterial number of 200 cfu/mL, the level at which the test panel could not yet diagnose the spoilage, indicating that the signals of e-nose could be applied as early indicators for the onset of spoilage. Sensors 2, 6, 7, and 8 were determined to be quite sensitive to the alteration of flavor in apple juice beverage and had played the most important part in discrimination. Furthermore, based on the response of e-nose, A. acidoterrestris counts in unknown samples could be well predicted by established partial least squares (PLS) regression model with a high relation of 0.95. Based on these results, e-nose can be employed as a powerful tool for quick and reliable analysis of the flavor in apple juice beverages during processing or on the shelf to implement rapid routine inspection as well as realize the early detection of potential spoilage caused by A. acidoterrestris.

Microcystis aeruginosa/Pseudomonas pseudoalcaligenes interaction effects on off-flavors in algae/bacteria co-culture system under different temperatures

We conducted an experiment to study the interaction effects of Microcystis aeruginosa and Pseudomonas pseudoalcaligenes on off-flavors in an algae/bacteria co-culture system at three temperatures (24, 28 and 32°C). Gas chromatography–mass spectrometry was applied to measure off-flavor compounds dimethyl sulfide (DMS), dimethyl trisulfide (DMTS), 2-methylisoborneol, geosmin (GEO) and β-cyclocitral. During the lag phase of co-cultured M. aeruginosa (first 15days), P. pseudoalcaligenes significantly increased the production of DMS, DMTS and β-cyclocitral at all three temperatures. In the exponential phase of co-cultured M. aeruginosa (after 15days), M. aeruginosa became the main factor on off-flavors in the co-culture system, and β-cyclocitral turned to the highest off-flavor compound. These results also indicated that DMS, DMTS and β-cyclocitral were the main off-flavor compounds in our M. aeruginosa/P. pseudoalcaligenes co-culture system. Univariate analysis was applied to investigate the effects of M. aeruginosa and P. pseudoalcaligenes on the production of off-flavors. The results demonstrated that both M. aeruginosa and P. pseudoalcaligenes could increase the production of DMS and DMTS, while β-cyclocitral was mainly determined by M. aeruginosa. Our results also provide some insights into understanding the relationship between cyanobacteria and heterotrophic bacteria.

Effect of Stocking Large Channel Catfish in a Biofloc Technology Production System on Production and Incidence of Common Microbial Off-Flavor Compounds

Density-dependent production and incidence of common microbial off-flavors caused by geosmin and 2-methylisoborneol were investigated in an outdoor biofloc technology production system stocked with stockersize (217 g/fish) channel catfish at 1.4, 2.1, or 2.8 kg/m3. Individual weight at harvest ranged from 658-829 g/fish and was inversely related to stocking density. Net fish yield ranged from 3.8-5.4 kg/m3, and increased linearly as stocking density increased. The percentage of sub-marketable fish (<0.57 kg/fish) increased linearly with increasing stocking rate. Mean total feed consumption increased linearly with stocking density, but feed consumed per fish was inversely related to stocking density. Feed conversion ratio did not differ significantly among treatments. Concentrations of geosmin and 2-methylisoborneol in biofloc water were low throughout the study. All sampled fillets contained low concentrations of geosmin and 2-methylisobornel, but these fillets likely would not be deemed as having objectionable “earthy” or “musty” off-flavors when evaluated by trained processing plant flavor testers because of the low concentrations present. Data from this study combined with data from our two previous studies provide strong evidence that the incidence of geosmin- and 2-methylisoborneol-related off-flavor episodes is low in the BFT production system.

Assessing genetic diversity among Brettanomyces yeasts by DNA fingerprinting and whole-genome sequencing.

Brettanomyces yeasts, with the species Brettanomyces (Dekkera) bruxellensis being the most important one, are generally reported to be spoilage yeasts in the beer and wine industry due to the production of phenolic off flavors. However, B. bruxellensis is also known to be a beneficial contributor in certain fermentation processes, such as the production of certain specialty beers. Nevertheless, despite its economic importance, Brettanomyces yeasts remain poorly understood at the genetic and genomic levels. In this study, the genetic relationship between more than 50 Brettanomyces strains from all presently known species and from several sources was studied using a combination of DNA fingerprinting techniques. This revealed an intriguing correlation between the B. bruxellensis fingerprints and the respective isolation source. To further explore this relationship, we sequenced a (beneficial) beer isolate of B. bruxellensis (VIB X9085; ST05.12/22) and compared its genome sequence with the genome sequences of two wine spoilage strains (AWRI 1499 and CBS 2499). ST05.12/22 was found to be substantially different from both wine strains, especially at the level of single nucleotide polymorphisms (SNPs). In addition, there were major differences in the genome structures between the strains investigated, including the presence of large duplications and deletions. Gene content analysis revealed the presence of 20 genes which were present in both wine strains but absent in the beer strain, including many genes involved in carbon and nitrogen metabolism, and vice versa, no genes that were missing in both AWRI 1499 and CBS 2499 were found in ST05.12/22. Together, this study provides tools to discriminate Brettanomyces strains and provides a first glimpse at the genetic diversity and genome plasticity of B. bruxellensis.

The effect of acidification of liquid whey protein concentrate on the flavor of spray-dried powder

Off-flavors in whey protein negatively influence consumer acceptance of whey protein ingredient applications. Clear acidic beverages are a common application of whey protein, and recent studies have demonstrated that beverage processing steps, including acidification, enhance off-flavor production from whey protein. The objective of this study was to determine the effect of preacidification of liquid ultrafiltered whey protein concentrate (WPC) before spray drying on flavor of dried WPC. Two experiments were performed to achieve the objective. In both experiments, Cheddar cheese whey was manufactured, fat-separated, pasteurized, bleached (250mg/kg of hydrogen peroxide), and ultrafiltered (UF) to obtain liquid WPC that was 13% solids (wt/wt) and 80% protein on a solids basis. In experiment 1, the liquid retentate was then acidified using a blend of phosphoric and citric acids to the following pH values: no acidification (control; pH 6.5), pH 5.5, or pH 3.5. The UF permeate was used to normalize the protein concentration of each treatment. The retentates were then spray dried. In experiment 2, 150μg/kg of deuterated hexanal (D12-hexanal) was added to each treatment, followed by acidification and spray drying. Both experiments were replicated 3 times. Flavor properties of the spray-dried WPC were evaluated by sensory and instrumental analyses in experiment 1 and by instrumental analysis in experiment 2. Preacidification to pH 3.5 resulted in decreased cardboard flavor and aroma intensities and an increase in soapy flavor, with decreased concentrations of hexanal, heptanal, nonanal, decanal, dimethyl disulfide, and dimethyl trisulfide compared with spray drying at pH 6.5 or 5.5. Adjustment to pH 5.5 before spray drying increased cabbage flavor and increased concentrations of nonanal at evaluation pH values of 3.5 and 5.5 and dimethyl trisulfide at all evaluation pH values. In general, the flavor effects of preacidification were consistent regardless of the pH to which the solutions were adjusted after spray drying. Preacidification to pH 3.5 increased recovery of D12-hexanal in liquid WPC and decreased recovery of D12-hexanal in the resulting powder when evaluated at pH 6.5 or 5.5. These results demonstrate that acidification of liquid WPC80 to pH 3.5 before spray drying decreases off-flavors in spray-dried WPC and suggest that the mechanism for off-flavor reduction is the decreased protein interactions with volatile compounds at low pH in liquid WPC or the increased interactions between protein and volatile compounds in the resulting powder.

Hydrolytic Enzyme Levels in Malted Cereals

Six grain samples namely barley, maize, millet, rice, sorghum and wheat were tested for enzyme levels (amylase, protease and lipase) in order to assess their malting characteristics, using barley as a standard. The levels of the enzymes were estimated in the whole dry grains, 24h steeped, 24h sprouted and 48h sprouted grains. A combined statistical analysis of linear regression and analysis of variance were used to test for enzyme interaction, similarities and interspecific relationship between the cereals. The estimated interspecific relationship between sorghum and barley was 84% based on the three enzymes, while millet had 75%. All the sprouted cereals with the exception of the standard barley had high lipase levels. This possibly suggests certain limitations as regards to production of off-flavours. Malt prepared from maize, sorghum, rice and millet had comparable protease levels with barley (P>0.05). The malts prepared from maize, millet, rice, sorghum and wheat had comparatively low alpha-amylase levels when compared with the standard barley. Multiple linear regressions showed amylase was dependent on lipase and protease. The relationship was not affected by either soaking (steeping) or sprouting of the grains. The implications of these findings suggest that a combination of these cereals might give good malt for food applications.