Analysis of factors affecting volatile compound formation in roasted pumpkin seeds with selected ion flow tube-mass spectrometry (SIFT-MS) and sensory analysis

Pumpkin (Cucurbita pepo and maxima) seeds are uniquely flavored and commonly consumed as a healthy roasted snack. The objective was to determine dominant volatiles in raw and roasted pumpkin seeds, and the effect of seed coat, moisture content, fatty acid ratio, total lipids, reducing sugars, and harvest year on volatile formation. Sensory was conducted to evaluate overall liking of seed variety and texture. Seed processing included extraction from the fruit, dehydration, and roasting (150 °C). Oil extraction was done using soxhlet, fatty acid profile using Gas Chromatography Flame Ionization Detector, and reducing sugars using 3,5-dinitrosalicylic acid and UV-spectroscopy. Headspace analysis of seeds was performed by selected ion flow tube-mass spectrometry (SIFT-MS). Volatiles dominating in raw pumpkin seeds were lipid aldehydes, ethyl acetate, 2,3-butandione, and dimethylsulfide. Compounds contributing to roasted aroma include alkylpyrazines and Strecker and lipid aldehydes. Overall, hull-less seeds had higher volatile lipid aldehydes and Strecker aldehydes. Seeds dehydrated to a moisture content of 6.5% before roasting had higher initial and final volatile concentrations than seeds starting at 50% moisture. Higher oil content resulted in higher lipid aldehyde formation during roasting with a moderate correlation between free fatty acid ratio and corresponding lipid aldehyde. Harvest year (2009 compared with 2010) had a significant impact on volatile formation in hull-less seeds, but not as much as variety differences. No significant correlation was found between reducing sugars and volatile formation. Sensory showed that hull-less seeds were liked significantly more than hulled seeds. PRACTICAL APPLICATION: Elucidation of aromatic flavor development during roasting with SIFT-MS provides information on flavor release and offers better control during processing. Knowledge of volatiles in raw and roasted pumpkin seeds and effects of seed coat, moisture content, seed composition, and harvest date will allow for better control over the production/storage/transportation process and a more educated decision during selection of a variety for production of pumpkin seeds in the snack food industry.     

Changes in polyphenol ability to produce astringency during roasting of cocoa liquor

Polyphenols in cocoa products determine the astringent sensation due to their interaction with salivary proline‐rich protein. Changes in the ability of polyphenols to produce astringency during cocoa roasting have been studied through an evaluation of the polyphenol–protein interaction in cocoa cake/liquor roasted at 120 °C for 45 min, with and without enrichment with polyphenol extract. Roasting decreased the capacity of polyphenols to interact with protein, causing a decrease in astringency. However, the polyphenol–protein interaction products after roasting could still be oxidized enzymatically and most probably would still give cocoa products beneficial effects as functional food. Copyright © 2005 Society of Chemical Industry     

Alkylpyrazines and Other Volatiles in Cocoa Liquors at pH 5 to 8, by Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS)

ABSTRACT:  Cocoa beans were alkalized before or after roasting and made into cocoa liquor before analyzing by SIFT-MS. In both alkalized-before-roasting and alkalized-after-roasting samples, there were significantly higher concentrations of alkylpyrazines for the samples with pH above 7 than pH below 7. At pH 8, the concentrations of 2,3-, 2,5-, and 2,6-dimethylpyrazine (DMP), 2,3,5-trimethylpyrazine (TrMP), 2,3,5,6-tetramethylpyrazine (TMP), and 2,3-diethyl-5-methylpyrazine (EMP) in the samples alkalized-before-roasting were higher than those in the samples alkalized-after-roasting. Volatiles increased under conditions that promoted the Maillard reaction. The partition coefficient was not significantly affected by pH from 5.2 to 8. The ratios of TrMP/DMP and DMP/TMP increased while the ratio of TMP/TrMP decreased as the pH increased. The concentrations of Strecker aldehydes and other volatiles followed a similar pattern as that of the alkylpyrazines. High pH favors the production of alkylpyrazines and Strecker aldehydes.
Practical Applications: Cocoa beans alkalized-before-roasting had higher levels of many important chocolate aroma volatiles than those alkalized-after-roasting. Thus, alkalizing before roasting should produce a stronger cocoa aroma. The higher the pH, the higher the concentrations of these important volatiles. There was little change in volatile concentration at acid pH. Above pH 7, volatile levels increased rapidly with increasing pH. To maintain the recommended ratio of tetramethylpyrazine to trimethylpyrazine, a longer roasting time or higher temperature is needed for cocoa liquor with a pH below 6.5, while a shorter roasting time or lower temperature is needed for cocoa liquor with a pH above 7.     

Effect of roasting conditions on color and volatile profile including HMF level in sweet almonds (Prunus dulcis)

Microwave, oven, and oil roasting of almonds were used to promote almond flavor and color formation. Raw pasteurized almonds were roasted in a microwave for 1 to 3 min, in an oven at 177 °C for 5, 10, 15, and 20 min; and at 135 and 163 °C for 20 min, and in oil at 135, 163, and 177 °C for 5 min and 177 °C for 10 min. Volatile compounds were quantified in the headspace of ground almonds, both raw and roasted, by selected ion flow tube mass spectrometry. Strong correlations were found between L value, chroma, and 5-(hydroxy methyl)-2- furfural; and were independent of roasting method. Raw almonds had lower concentrations of most volatiles than roasted almonds. Conditions that produced color equivalent to commercial samples were 2 min in the microwave, 5 min at 177 °C in the oven, and 5 min at 135 °C in oil. Microwave heating produced higher levels of most volatiles than oven and oil roasting at commercial color. Sensory evaluation indicated that microwave-roasted almonds had the strongest aroma and were the most preferred. Oil-roasted almonds showed significantly lower levels of volatiles than other methods, likely due to loss of these volatiles into the oil. Alcohols such as benzyl alcohols and strecker aldehydes including benzaldehyde and methional were at higher concentrations than other volatiles in roasted almonds. The oxidation of lipids to form alkanals such as nonanal and degradation of sugars to form furan type compounds was also observed. The Maillard reaction contributed to the formation of more of the total volatiles in almonds than the lipid oxidation reaction. PRACTICAL APPLICATION: The level of 5-(hydroxy methyl)-2- furfural (HMF), color, volatile profile, and sensory perception can be used to develop the best roasting method, time, and temperature for almonds. The rate of color development and the production of volatiles differ under different roasting conditions. Based on the color, volatile, and sensory assessments of the 3 almonds, the use of microwave technology as a process for roasting almonds reduces processing time and leads to an almond product with better flavor than oven or oil roasting.     

Effect of glucose and glycine addition to cocoa mass before roasting on Maillard precursor consumption and pyrazine formation

Cocoa mass was treated with glucose and/or glycine before roasting. For glucose‐treated samples the reductions in reducing sugars and free amino acids were 41.1 and 56.9% respectively, whereas for glycine‐treated samples the respective reductions were 16.2 and 37.4%. The combination of glucose plus glycine treatment led to 39.0 and 48.9% reductions in reducing sugars and free amino acids respectively. For free amino acids the reductions in control and glucose‐treated samples were similar, 56.2 and 56.9% respectively, indicating that the added glucose did not significantly (P < 0.05) influence the free amino acid uptake. When glycine was added, the consumption of free amino acids (37.4%) was lower than for the control and glucose treatments. When glucose and glycine were added, the reduction in free amino acids (48.9%) was lower than for the control and glucose treatments but higher than for the glycine treatment. Apparently, glycine addition inhibited the reducing sugar and free amino acid consumption, whereas glucose addition enhanced the reducing sugar and free amino acid consumption. The glucose plus glycine treatment was similar to the glycine treatment in the contents of 2,5‐dimethyl‐ and trimethylpyrazines. For 2‐methylpyrazine the value for glucose‐treated samples was lower than for control and glycine‐treated samples but almost equal to the value for the glucose plus glycine treatment. It is concluded that the addition of glucose and/or glycine does not affect pyrazine production. © 2002 Society of Chemical Industry     

Structural and chemical changes in cocoa (Theobroma cacao L) during fermentation,drying and roasting

Cocoa seeds and pulp were fermented for 144 h, followed by natural drying. The tegument was removed and the cotyledons were broken into nibs which were roasted at 150 °C for 30 min. Non‐fermented material, material fermented for 24, 48 and 72 h, material fermented for 144 h and then dried, and also the roasted nibs, were all prepared for chemical and microscopic analyses. Light microscopy revealed the presence of anionic and cationic residues and of neutral sugars. During fermentation there was a reduction in the cytoplasmic content of phenolic compounds and in the number of protein bodies. The cell wall showed a reduction in anionic residues and a loss of crystallinity. These alterations were maximum after 72 h. Drying and roasting increased the number of damaged cells and reduced the amount of cytoplasmic material. The chemical analyses generally confirmed the microscopy results. The concentration of amino‐terminal groups and total free amino acids increased during fermentation (up to 72 h), but returned to the initial values after roasting. The principal chemical changes were related to reducing sugars, free amino acids, proteins and phenols, and PCA was suggested as a useful tool to compare different samples. Microscopic analysis revealed the degradation of protein and phenolic bodies and cellular damage during roasting. © 2000 Society of Chemical Industry     

Volatile profile of cashews (Anacardium occidentale L.) from different geographical origins during roasting

Abstract: Volatile compounds were quantified in the headspace of Indian, Vietnamese, and Brazilian cashews, both raw and during roasting by selected ion flow tube‐mass spectrometry. The optimum roasting times based on color measurements were also determined. Raw cashews were oil roasted for 3 to 9 min at 143 °C and color and volatiles measured. An excellent correlation, following a pseudo 1st‐order reaction, was found between L* value and roasting time; darkness increases as roasting time increases. The optimum roasting time was 6, 8, and 9 min for Vietnamese, Indian, and Brazilian cashews, respectively. Raw cashews had lower concentrations of volatiles than roasted cashews. Most volatiles significantly increased in concentration during roasting of Brazilian, Indian, and Vietnamese cashews. Only a few volatiles significantly decreased during roasting. Ethanol and 1‐heptene significantly decreased during roasting in Brazilian cashews and toluene decreased in Vietnamese cashews. Brazilian cashews had significantly higher levels of most volatiles than Indian and Vietnamese cashews. Most volatile levels in Indian and Vietnamese cashews were not significantly different. Of the volatiles, Strecker aldehydes, including methylbutanal, 2‐methylpropanal, and acetaldehyde, were at the highest concentration in roasted cashews. The Maillard reaction contributed to the formation of most of the volatiles in cashews from the 3 countries. There was also degradation of sugars to form furan‐type compounds and oxidation of lipids to form alkanals such as hexanal. Practical Application: The volatile profile during roasting of cashews can be used to determine the best roasting time for each type of cashew. The rate of color development and the production of volatiles differ for the cashews from the 3 geographical locations.     

Effect of roasting time and temperature on volatile component profiles during nib roasting of cocoa beans (Theobroma cacao)

The effect of nib roasting time and temperature on volatile component profiles was studied using response surface methodology (RSM) which consisted of two independent variables: time (5–65 min) and temperature (110–170°C). A steam distillation extraction (SDE) method was used to extract and gas chromatograph–mass spectrometry equipped with an ICIS data system was used to identify the volatile compounds. Tetramethylpyrazine, trimethylpyrazine, phenethyl acetate, isoamyl acetate, 3-methylbutyl acetate, phenylacetaldehyde, benzaldehyde and 2-phenylethanol were present in all treatments. Pyrazine formation increased as roasting time and temperature were increased. The number of pyrazines increased from 4 to 11 and 25, respectively, when roasting, time was increased from 5 to 35 and 65 min at 140°C. The unit area of esters increased (up to 1700–1800) when the roasting time was increased from 15 to 65 min (at 110–120°C). However, the unit area of carbonyls linearly decreased with an increasing roasting temperature at shorter time (5–25 min). The unit area of phenols was enormously reduced at the highest roasting temperature (160–170°C) with longest roasting time (45–65 min) while that of alcohol slightly decreased as roasting time and temperature were increased. © 1998 SCI.     

Application of solid phase-microextraction (SPME) and electronic nose techniques to differentiate volatiles of sesame oils prepared with diverse roasting conditions

Headspace volatiles of sesame oil (SO) from sesame seeds roasted at 9 different conditions were analyzed by a combination of solid phase microextraction (SPME)-gas chromatography/mass spectrometry (GC/MS), electronic nose/metal oxide sensors (MOS), and electronic nose/MS. As roasting temperature increased from 213 to 247 °C, total headspace volatiles and pyrazines increased significantly (P < 0.05). Pyrazines were major volatiles in SO and furans, thiazoles, aldehydes, and alcohols were also detected. Roasting temperature was more discrimination factor than roasting time for the volatiles in SO through the principal component analysis (PCA) of SPME-GC/MS, electronic nose/MOS, and electronic nose/MS. Electronic nose/MS showed that ion fragment 52, 76, 53, and 51 amu played important roles in discriminating volatiles in SO from roasted sesame seeds, which are the major ion fragments from pyrazines, furans, and furfurals. SO roasted at 213, 230, and 247 °C were clearly differentiated from each other on the base of volatile distribution by SPME-GC/MS, electronic nose/MOS, and electronic nose/MS analyses. Practical Application: The results of this study are ready to apply for the discriminating samples using a combinational analysis of volatiles. Not only vegetable oils prepared from roasting process but also any food sample possessing volatiles could be targets for the SPME-GC/MS and electronic nose assays. Contents and types of pyrazines in sesame seed oil could be used as markers to track down the degree of roasting and oxidation during oil preparation.     

亚麻籽炒籽过程美拉德反应底物变化及其模拟体系产物的抗氧化活性北大核心CSCD

为研究亚麻籽热榨过程中美拉德反应形成的物质类型及其抗氧化效果,以亚麻籽为原料,在120~200℃下炒籽10~30 min并提取亚麻籽油,考察不同炒籽条件下亚麻籽油的氧化稳定性,分析炒籽前后亚麻籽脱脂粉中还原糖和游离氨基酸含量变化,确定美拉德模拟体系的反应底物。以抗氧化活性为指标,对美拉德模拟反应条件进行优化,并考察美拉德反应产物(MRPs)对冷榨亚麻籽油氧化稳定性的影响。结果表明:在180℃条件下炒籽20 min制备的亚麻籽油氧化稳定性最好;美拉德模拟反应的最优条件为葡萄糖与赖氨酸物质的量比3∶1、反应温度180℃、反应时间105 min和葡萄糖与精氨酸物质的量比1∶1、反应温度180℃、反应时间105 min;两种MRPs对冷榨亚麻籽油过氧化值增长没有明显的抑制效果,而对p-茴香胺值的增长有一定的抑制作用。赖氨酸、精氨酸和葡萄糖的美拉德反应对提高热榨亚麻籽油的氧化稳定性起关键作用,其MRPs对冷榨亚麻籽油具有一定的抗氧化作用。     

Proteolytic activity (aspartic endoproteinase and carboxypeptidase) of cocoa bean during fermentation

This study was carried out to examine the changes in cocoa aspartic endoproteinase and carboxypeptidase activities, mass pH and temperature during 144 h (6 days) of fermentation using shallow wooden boxes. The results showed that at 72 h of fermentation, the activity of aspartic endoproteinase was higher than the original value. However, at 96 h the carboxypeptidase activity was higher than its original activity. The study also found a high correlation 0·99 (P<0·05) between the mass temperature with the aspartic endoproteinase at 48 h of fermentation. No correlation was found between the mass pH and temperature with the carboxypeptidase during fermentation. The degradation of vicilin-class globulin was about 88·8% and that of albumin was 47·4% at the end of fermentation. © 1998 SCI.     

多次顶空萃取-选择离子流动管-质谱法测定食用油中呋喃的气液分配系数

呋喃属于食品热加工过程中产生的潜在致癌物。为准确测定呋喃在食用油中的气液分配系数,采用多次顶空萃取-选择离子流管-质谱法测定封闭体系顶空中的呋喃含量,并根据分配系数定义和多次顶空萃取过程,建立了测定油中呋喃分配系数的数学关系式。结果表明,澳洲坚果油、大豆油、花生油、橄榄油中呋喃的分配系数为338.5、336.4、357.6、365.6(60℃时)。该方法具有良好的精密度(RSD6.1%)和准确度,且简单、实用、不需要呋喃标样,所获得的数学关系式可作为其他挥发性成分分配系数测定的参考。     

Influence of sodium chloride on colour,residual volatiles and acrylamide formation in model systems and breakfast cereals

To elucidate the salt action in breakfast cereals to decrease its amount without a quality loss, a model system was developed. This model, composed of native maize starch, glucose and a mixture of five amino acids (glucose/amino acids molar ratio = 1/1) generated similar colour and volatiles (m/z = 45, 59, 69, 73, 87 and 103 g mol^?1) after heating compared to commercial breakfast cereals. A designed experiment used this model to study the influence of salt concentration (0–5.44%), heating time (0–25 min) and temperature (180–230 °C) on colour, residual volatiles and acrylamide formation. The higher the salt concentration, heating time and temperature, the darker were the products (P < 0.05). The L* values of the model systems containing 5 % salt and heated for 25 min at 230 °C were twelve points lower than the same systems without salt heated in the same conditions. Presence of salt significantly decreased acrylamide formation in the model systems (up to 50 % decrease when 2.5 % salt is added). However, salt did not have a significant impact on volatile levels. These findings were confirmed by observations made on four types of commercial breakfast cereals.     

Selective removal of the violet color produced by anthocyanins in procyanidin-rich unfermented cocoa extracts

Abstract: Cacao (Theobroma cacao L.) is rich in procyanidins, a large portion of which degrades during the natural fermentation process of producing cocoa powder. Recent advances in technology have enabled scientists to produce unfermented cocoa powder, preserving the original profile of procyanidins present in cocoa and allowing for the development of highly concentrated procyanidin‐rich extracts. During this process, the anthocyanins naturally present in unfermented cocoa remain intact, producing a violet color in the final extract. The objective of this study was to selectively remove the violet color in procyanidin‐rich extracts produced from unfermented cocoa powder, while maintaining the stability and composition of procyanidins present in the matrix. Several processing parameters, including pH fluctuations, enzymatic treatments, and the addition of potassium meta‐bisulfite, were explored to influence the color of procyanidin‐rich extracts throughout a 60‐d shelf life study. The addition of potassium meta‐bisulfite (500 ppm) was found to be the most effective means of removing the violet color present in the treated extracts (L*= 71.39, a*= 8.44, b*= 9.61, chroma = 12.79, and hue = 48.8?) as compared to the control (L*= 52.84, a*= 11.08, b*= 2.24, chroma = 11.28, and hue = 11.4?). The use of potassium meta‐bisulfite at all treatment levels (200, 500, and 1000 ppm) did not show any significant detrimental effects on the stability, composition, or amount of procyanidins present in the extracts over the shelf life period as monitored by UV‐Vis spectrophotometry and HPLC‐MS. This research will enable the food industry to incorporate highly concentrated procyanidin‐rich extracts in food products without influencing the color of the final product.     

Changes in volatile compounds of peanut oil during the roasting process for production of aromatic roasted peanut oil

The changes in volatile compounds composition of peanut oil during the roasting process of aromatic roasted peanut oil (ARPO) production were investigated. The analyses were performed by gas chromatography-mass spectrometry combined with headspace solid phase microextraction (HS-SPME/GC-MS). Among the volatiles identified in ARPO, the N-heterocyclic chemical class possessed the highest relative percentage area (RPA) 61.68%, followed by O-heterocyclic group with an RPA of 24.57%. Twenty pyrazines were considered to be the key contributors to the intense nutty/roasty flavor typical of ARPO. Compounds that increased significantly in concentration during the roasting process were mainly Maillard reaction products, as well as compounds derived from Strecker degradation and lipid peroxidation. The results clearly showed that the roasting process was necessary to obtain the typical nutty/roasty aroma of ARPO. PRACTICAL APPLICATION: ARPO is the traditional edible oil in China that possesses a characteristic strong nutty and roasty flavor that distinguishes it from other edible vegetable oils. During the production, the roasting process is the crucial factor for the formation of the typical roasted peanut aroma that plays an important role in sensory quality of peanut oil. In our investigation, not only the volatile changes of peanut oil pressed from relevant peanut seeds roasted at different roasting time were determined, but also the contributions of identified volatiles on the typical nutty/roasty flavor of ARPO were discussed. Our work clearly demonstrated the significant effect of roasting process on the typical flavor formation of ARPO. The results are valuable as scientific guidance for the roasting process that better satisfy demands of the peanut oil industries for better flavor.     

Volatile generation in bell peppers during frozen storage and thawing using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS)

To determine volatile formation during storage and thawing, whole, pureed, blanched, and raw green and red bell peppers (Capsicum annuum) were frozen quickly or slowly then stored at -18 °C for up to 7 mo, with and without SnCl(2) addition during thawing. Headspace analysis was performed by a Selected Ion Flow Tube Mass Spectrometer (SIFT-MS). After blanching, (Z)-3-hexenal had a large significant decrease in concentration since it is a heat labile compound while most other volatiles did not change in concentration. The freezing process increased volatile levels in the puree only. Slow freeze peppers had higher levels of some LOX generated volatiles during storage than quick freeze. During frozen storage of blanched samples (E)-2-hexenal, (Z and E)-hexen-1-ol, and (E)-2-pentenal increased likely because of nonenzymatic autoxidation of fatty acids while other volatiles remained constant. In Raw Whole peppers, (Z)-3-hexenal, hexanal, and 2-pentylfuran were generated during storage likely because the LOX enzyme is still active during frozen storage. However, blanched samples had higher concentrations of (E)-2-hexenal, (Z and E)-hexen-1-ol, 1-penten-3-one, and (E)-2-heptenal because of enzymatic destruction of these volatiles in the raw samples. The levels of many of the volatiles in the raw samples, including (Z)-3-hexenal, (E)-2-hexenal, (Z and E)-hexen-1-ol, hexanal, (E)-2-pentenal, and 2-pentylfuran, appeared to peak around 34 d after freezing. Pureed samples had significantly higher levels of volatiles than the whole samples, and volatiles peaked earlier. Green bell pepper volatile levels were always higher than red bell pepper. Significantly higher volatile formation occurred during thawing than it did during frozen storage. Practical Application: Studying and monitoring the headspace volatiles with a SIFT-MS can give information that will help manufacturers better understand how the volatiles in bell peppers change during frozen storage. This will give valuable information to processors on how to minimize volatile changes during storage of frozen peppers.     

GC-MS法测定侧流卷烟烟气中挥发性化合物

采用鱼尾罩和装有剑桥滤片的捕集装置将侧流烟气中的5种挥发性化合物（1,3-丁二烯、异戊二烯、丙烯腈、苯、甲苯）捕集于甲醇溶液中, 采用四极杆GC-MS结合质谱选择性离子扫描模式（SIR）定量测定侧流卷烟烟气中5种挥发性化合物释放量。试验证明,此方法有较好的重复性:对5种挥发性化合物释放量组内测定的RSD≤3.45%,组间测定RSD≤6.27%;具有较高的灵敏度:5种挥发性化合物的检测限均低于0.13 μg /支;较高的准确性:5种挥发性化合物的回收率在93.37%～98.2%之间。      

Effect of roasting on colour and volatile composition of pistachios (Pistacia vera L.)

Pistachios have been roasted following the Iranian traditional method (soaking in salty water, drying and roasting at 135 °C). Three Iranian pistachio cultivars (Ahmad Aghaei, Akbari and Kaleghouchi) were compared for their volatile compositions, colour and odour intensity. Lightness decreased in the course of roasting, which resulted from Maillard reaction. Raw pistachios had lower concentrations of most volatiles than roasted. A total of twenty‐six compounds were detected in roasted pistachios; these included aldehydes, terpenes, alcohols and only two pyrazines and one furan. These mixtures of volatiles implied that the Iranian roasting system is very soft, and samples retained most of the vegetable notes from fresh pistachios and some roasted notes were generated as well (from 2‐ethyl‐5‐methylpyrazine and 2,6‐dimethyl‐3‐ethylpyrazine). Sample from cultivar Akbari presented higher odour intensity than those by the other two cultivars, due mainly to higher concentrations of pyrazines developed during the roasting step.     

Carbohydrate composition and color development during drying and roasting of macadamia nuts (Macadamia integrifolia)

Research was conducted to determine whether variability in sugar content contributes to differences in kernel browning during processing of macadamia nut (Macadamia integrifolia) cultivars, Kau (HAES 344), Keaau (HAES 660), Keauhou (HAES 246), and Kakea (HAES 508). At harvest, total sugar content of fresh macadamia kernels varied from 2.9 to 5.6 g/100 g dry weight basis (db), and the average moisture content ranged from 15.6 to 23.6 g/100 g fresh weight. Cultivars differed in kernel sucrose content, but not reducing sugar content. Reducing sugars decreased during drying, and kernel centers darkened slightly. An incremental drying process limited sucrose hydrolysis, minimizing the amount of glucose and fructose available for browning reactions. Therefore, the centers of roasted kernels were not darker than dried kernels. The variability in sugar composition in fresh kernels had a minimal impact on color quality when low-temperature drying and roasting at 125 °C were used. However, when roasted kernels received from a processor were separated based on color quality, kernels with internal or external browning had higher reducing sugar concentrations (0.24-0.27 g/100 g db) than cream-colored kernels (0.03 g/100 g db). Immature kernels had higher sucrose and reducing sugar contents and more browning than mature kernels. During commercial processing, optimal conditions may not be achieved and the presence of immature nuts can contribute to kernel browning.     

(E)-2-庚烯醛对半胱氨酸-木糖体系美拉德反应产物的影响

研究了脂类氧化产物(E)-2-庚烯醛对L-半胱氨酸与D-木糖组成的美拉德反应体系热反应产物的影响。加入(E)-2-庚烯醛时,热反应产物在294 nm和420 nm处的吸光值均增大。采用固相微萃取结合气质联用法对不同模型体系热反应挥发性产物进行分析,结果表明,添加(E)-2-庚烯醛的美拉德反应产物中含氮、含硫化合物的形成受到抑制,一些硫醇类、噻吩类、噻唑类等硫化物的含量都有一定程度的减少,尤其是2-甲基-3-呋喃硫醇、2-糠硫醇、3-甲基噻吩和2,5-噻吩二甲醛的含量明显下降。随着(E)-2-庚烯醛含量的增加,生成了一些新的烷基噻吩类,如2-己基噻吩、2-(1,1-二甲基乙基)-噻吩和5-甲基-2-噻吩甲醛等。并且与对照相比,加入(E)-2-庚烯醛的体系新增了一些的醇类、酮类和酯类物质。