Evaluation of 2-acetyl-1-pyrroline in foods, with an emphasis on rice flavour

Comprehensive multi-layered analyses of genotype-dependent proteo-metabolic networks reveal organellar crosstalk and biochemical pathways regulating aroma formation in rice

Molecular basis of rice aroma formation is sparsely known and developmental programs driving biochemical pathways towards aroma is in infancy. Here, discovery and targeted proteo-metabolome of non-aromatic and aromatic rice seeds across developmental stages identified a total of 442 aroma-responsive proteins (ARPs) and 824 aroma-responsive metabolites (ARMs) involved in metabolism, calcium and G-protein signaling. Biochemical examination revealed ARM/Ps were linked to 2-acetylpyrrolidine, γ-aminobutyrate, anthocyanin, tannins, flavonoids and related enzymes. Pairwise correlation and clustering showed positive correlation among ARM/Ps. Consistent with aroma-related QTLs, ARPs were mapped on chromosomes 3,4,5,8 and were mainly compartmentalized in cytoplasm and mitochondria. ARM/P-correlation network identified associations related to metabolism and signaling. Multiple reaction monitoring (MRM) confirmed role of catechins, quinic acid and quercetin in aroma formation. Pathway enrichment, multivariate analysis and qRT-PCR validated that calcium and G-protein signaling, aromatic/branched-chain aminoacid, 2-acetylpyrrolidine, oxylipin, melvonate and prenylpyrophosphate pathways, indole, phenylacetate, flavonoid, cinnamoic ester govern aroma formation in rice.

The kinetic study of 2-acetyl-1-pyrroline accumulation in the model system: An insight into enhancing rice flavor through the Maillard reaction

Controlling the Maillard reaction may affect the generation of 2-acetyl-1-pyrroline, the key aroma compound in rice. In this study, the kinetics of 2-acetyl-1-pyrroline accumulation in the glucose/proline model system was comprehensively investigated and extra methylglyoxal or glyoxal was added to enhance 2-acetyl-1-pyrroline concentrations during rice cooking. Using the multi-response kinetic modeling to derive kinetic parameters, the formation of glyoxal, as the reactive intermediate, was rate-determining for the overall generation rate of 2-acetyl-1-pyrroline. Besides, although 2-acetyl-1-pyrroline generation was easier to occur with lower activation energy, much higher depletion rates of 2-acetyl-1-pyrrroline at 120 °C and 140 °C led to maximal 2-acetyl-1-pyrroline accumulation at the lower temperature of 100 °C. Furthermore, the inclusion of 0.05 μmol/kg additional methylglyoxal in cooked rice significantly enhanced 2-acetyl-1-pyrroline generation. The work suggested that the development of rice products with superior flavor quality may be achieved by the slight accumulation of intermediates prior to thermal processing.

Progresses in biosynthesis pathway, regulation mechanism and potential application of 2-acetyl-1-pyrroline in fragrant rice

The formation of rice aroma is a complex process that is influenced by genetic and environmental factors. More than 500 fragrance compounds have been documented in fragrant rice, among which 2-AP dominates the aroma of rice. This paper introduced the identification of OsBadh2 in the biosynthesis of 2-AP in rice. Then, non-enzymatic and enzymatic pathways of the 2-AP biosynthesis have been comprehensively investigated. In detail, 2-AP biosynthesis-associated enzyme, such as OsBADH2, OsP5CS, OsGAD, OsGAPDH, OsProDH, OsOAT, OsODC and OsDAO, have been summarized, while MG and fatty acids are also implicated in modulating the biosynthesis of 2-AP by providing the acetyl groups. Moreover, extensive collections of traditional fragrant rice varieties have been collated, together with the OsBadh2 haplotypes of 312 fragrant rice germplasm in China. And finally, genetic engineering of OsBadh2 and other genes in the 2-AP biosynthesis to develop fragrant rice are discussed.

Analysis of mousy off-flavor compound 2-Acetyl-tetrahydropyridine using Liquid Chromatography Mass Spectrometry with Electrospray Ionization in sour beer

Mousy off-flavor describes N-heterocycles compounds related to spoilage in the brewing industry. It has also been identified in sour beers through sensory analysis. Therefore, preventing spoilage N-heterocycles development is essential to preserve end-products and obviate economic losses. To this day, no methods or protocols have been reported to identifying mousy off-flavor compounds in a beer matrix. The main objective of this work was to develop a standardized quantification method for 2-acetyl-3,4,5,6-tetrahydropyridine (ATHP) in beer matrix, by Liquid Chromatography Mass Spectrometry with Electrospray Ionization (LC-MS-ESI). Extraction of ATHP in the samples was performed using QuEChERS (quick, easy, cheap, effective, rugged, and safe) technique. Over a dozen different potentially mousy cask-aged sour beers including other spontaneously fermented beverages were provided, based on sensory analysis, to determine the variation in ATHP levels. Results indicated ATHP was found in all the samples, ranging from 1.64 ± 0.06 to 57.96 ± 2.15 µg L-1. Herein, we described our detection method of mousy-off flavor compounds which enables future research to mitigate the occurrence of such defects in fermented beverages matrix.•ATHP content in samples varied from 1.64 ± 0.06 to 57.96 ± 2.15 µg L-1.•The recovery range of ATHP using LC-MS-ESI varied from 71% to 97%.•Basified QuEChERS salting-out procedure is applicable for ATHP extraction from beer and other fermented beverages matrices.

A Review of N-Heterocycles: Mousy Off-Flavor in Sour Beer

Beer has over 600 flavor compounds and creates a positive tasting experience with acceptable sensory properties, which are essential for the best consumer experience. Spontaneous and mixed-culture fermentation beers, generally classified as sour beers, are gaining popularity compared to typical lager or ale styles, which have dominated in the USA for the last few decades. Unique and acceptable flavor compounds characterize sour beers, but some unfavorable aspects appear in conjunction. One such unfavorable flavor is called "mousy". This description is usually labeled as an unpleasant odor, identifying spoilage of fermented food and beverages. It is related as having the odor of mouse urine, cereal, corn tortilla chips, or freshly baked sour bread. The main compounds responsible for it are N-heterocyclic compounds: 2-acetyltetrahydropyridine, 2-acetyl-1-pyrroline, and 2-ethyltetrahydropyridine. The most common beverages associated with mousy off-flavor are identified in wines, sour beers, other grain-based beverages, and kombucha, which may contain heterofermentative lactic acid bacteria, acetic acid bacteria, and/or yeast/fungus cultures. In particular, the fungal species Brettanomyces bruxellensis are associated with mousy-off flavor occurrence in fermented beverages matrices. However, many factors for N-heterocycle formation are not well-understood. Currently, the research and development of mixed-cultured beer and non/low alcohol beverages (NABLAB) has increased to obtain the highest quality, sensory, functionality, and most notably safety standards, and also to meet consumers' demand for a balanced sourness in these beverages. This paper introduces mousy off-flavor expression in beers and beverages, which occurs in spontaneous or mixed-culture fermentations, with a focus on sour beers due to common inconsistency aspects in fermentation. We discuss and suggest possible pathways of mousy off-flavor development in the beer matrix, which also apply to other fermented beverages, including non/low alcohol drinks, e.g., kombucha and low/nonalcohol beers. Some precautions and modifications may prevent the occurrence of these off-flavor compounds in the beverage matrix: improving raw material quality, adjusting brewing processes, and using specific strains of yeast and bacteria that are less likely to produce the off-flavor. Conceivably, it is clear that spontaneous and mixed culture fermentation is gaining popularity in industrial, craft, and home brewing. The review discusses important elements to identify and understand metabolic pathways, following the prevention of spoilage targeted to off-flavor compounds development in beers and NABLABs.

Physical and Chemical Properties, Flavor and Organoleptic Characteristics of a Walnut and Purple Rice Fermented Plant Drink

In recent years, green and healthy foods have attracted much attention. Plant-based foods have become an alternative to animal-derived foods. In this study, we used walnut and purple rice as the primary raw materials to produce a fermented plant drink. The process included boiling, mixing, grinding, inoculation, fermentation, and sterilization. We then analyzed the similarities and differences between the resulting walnut and purple rice fermented plant drink and an unfermented walnut and purple rice plant drink, as well as dairy-based yoghurt, in terms of physical chemistry, flavor, and sensory characteristics. We also examined the similarities and differences between the walnut and purple rice fermented plant drink and room-temperature yoghurt. The study results revealed that the walnut and purple rice fermented plant drink exhibited greater viscosity than the walnut and purple rice unfermented plant drink and room-temperature yoghurt. Additionally, the former displayed enhanced stability and recovery ability. Notably, distinguishable differences were observed between the three samples in terms of the presence of unknown volatiles and the umami signal, as indicated by electronic nose/tongue and GC-IMS analyses. The umami flavor of the walnut and purple rice fermented plant drink surpasses that of room-temperature yoghurt, while its taste is less salty than that of the walnut and purple rice plant drink. Despite possessing a weaker aroma than dairy-based yogurt, it is more potent than the walnut and purple rice plant drink. Additionally, its relative abundance of olefins, ketones, and alcohols enhances its unique flavor profile, surpassing both other options. Based on sensory analysis, it can be deduced that walnut and purple rice fermented plant drink has the highest overall acceptance rate.

Discussion on the Differences in Aroma Components in Different Fragrant Rice Varieties during Storage

Rice (Oryza sativa L.) is an important food crop in Taiwan, among which fragrant rice is highly regarded for its special aroma when cooked. During the storage of fragrant rice, the aroma components will change, which will affect the aroma quality of fragrant rice. Therefore, headspace solid-phase microextraction (HS-SPME) was used in this study, combined with gas chromatography and gas chromatography-mass spectrometry, to analyze the difference in the aroma components of Taikeng No. 4 (TK4), Tainung No. 71 (TN71), Kaohsiung No. 147 (KH147), and Taichung No. 194 (TC194) fragrant rice. A total of 28 aroma components were identified in the four varieties of fragrant rice, and the main components were all Nonanal. Among them, TK4 contains a very high content of hydrocarbons, including Tridecane and Dodecane; TN71, KH147, and TC194 contain mainly aldehydes such as Nonanal and Hexanal. During different storage times, the contents of alcohols, monoterpenes, aromatic aldehydes, and furans increased with storage time, while the content of aliphatic aldehydes decreased with storage time. After storage, the fragrant rice samples showed a tendency for the total volatile component content to decrease, with the most pronounced reduction observed in Nonanal content.

Study on the degradation and pyrolysis of 2-fluoromethcathinone

Gas chromatography-mass spectrometry (GC-MS) is the first choice for law enforcement agencies in various countries to analyze new psychoactive substances (NPS) because of its advantages and complete databases. For synthetic cathinone-type NPS (SCat), alkalization and extraction processes before GC-MS analysis are essential. However, the base form of SCat is unstable, causing it to quickly degrade in solution and cause pyrolysis at the GC-MS injection inlet. In this study, we investigated the degradation of ethyl acetate and pyrolysis at the GC-MS injection inlet of 2-fluoromethcathinone (2-FMC), the most unstable SCat. Using gas chromatography-quadruple/time-of-flight mass spectrometry (GC-Q/TOF-MS) combined with the predicted data from theoretical calculations and the analysis of mass spectrometry (MS) fragmentation, the structures of 15 2-FMC degradation and pyrolysis products were identified. Among them, 11 products were produced during degradation, and six products were obtained from pyrolysis (two of which were the same as the degradation products). At the same time, the degradation and pyrolysis pathways of 2-FMC were provided. The balance between keto-enol and enamine-imine tautomerism triggered the primary degradation pathway of 2-FMC. The subsequent degradation started from the tautomer with a hydroxyimine structure, including imine hydrolysis, oxidation, imine-enamine tautomerism, intramolecular ammonolysis of halobenzene, and hydration to generate a series of degradation products. The secondary degradation reaction was the ammonolysis of ethyl acetate to yield N-[1-(2'-fluorophenyl)-1-oxopropan-2-yl]-N-methylacetamide and the byproduct, N-[1-(2'-fluorophenyl)-1-oxopropan-2-yl]-N-methylformamide. In the pyrolysis of 2-FMC, the major reactions were dehydrogenation, intramolecular ammonolysis of halobenzene, and defluoromethane. The achievements of this manuscript not only study 2-FMC degradation and pyrolysis but also lay the foundation for the study of SCat stability and their accurate analysis by GC-MS.

Analysis of volatile compounds by GCMS reveals their rice cultivars

Due to the similarity in the grain and difference in the market value among many rice varieties, deliberate mislabeling and adulteration has become a serious problem. To check the authenticity, we aimed to discriminate rice varieties based on their volatile organic compounds (VOCs) composition by headspace solid phase microextraction (HS-SPME) coupled with gas chromatography mass spectrometry (GC-MS). The VOC profiles of Wuyoudao 4 from nine sites in Wuchang were compared to 11 rice cultivar from other regions. Multivariate analysis and unsupervised clustering showed an unambiguous distinction between Wuchang rice and non-Wuchang rice. Partial least squares discriminant analysis (PLS-DA) demonstrated a goodness of fit of 0.90 and a goodness of prediction of 0.85. The discriminating ability of volatile compounds is also supported by Random forest analysis. Our data revealed eight biomarkers including 2-acetyl-1-pyrroline (2-AP) that can be used for variation identification. Taken together, the current method can readily distinguish Wuchang rice from other varieties which it holds great potential in checking the authenticity of rice.

Foliar methyl jasmonate (MeJA) application increased 2-acetyl-1-Pyrroline (2-AP) content and modulated antioxidant attributes and yield formation in fragrant rice

Endogenous methyl jasmonate (MeJA) mediates abiotic and biotic stresses in plants. Exogenous MeJA application can stimulate and defend plant gene expression and induce plant chemical defense. The effects of foliar MeJA application on yield and 2-acetyl-1-pyrroline (2-AP) biosynthesis of fragrant rice are scarcely investigated. The pot experiment was conducted by spraying different concentrations of MeJA (0, 1, and 2 μM; denoted as CK, MeJA-1, and MeJA-2) at the initial heading stage of two fragrant rice cultivars, Meixiangzhan and Yuxiangyouzhan. The results showed that foliar MeJA application significantly increased the grain 2-AP content by 32.1% and 49.7%, respectively, following MeJA-1 and MeJA-2 treatments, and the two cultivars showed the highest 2-AP content upon MeJA-2 treatment. However, the grain yield was increased in MeJA-1 as compared with MeJA-2 treatment for all rice cultivars and no significant differences were observed in yield and yield-related traits compared with CK. The aroma was improved by foliar MeJA application which was strongly associated with the regulation of the precursors and enzymes involved in 2-AP biosynthesis. In particular, the contents of proline, pyrroline-5-carboxylic acid, and pyrroline at maturity, as well as the activities of proline dehydrogenase, ornithine aminotransferase, and pyrroline-5-carboxylic acid synthetase, were positively correlated with grain 2-AP content. On the other hand, foliar MeJA application improved the contents of soluble protein, chlorophyll a and b, and carotenoid, and increased the activity of antioxidant enzymes. Moreover, peroxidase activity and leaf chlorophyll contents were significantly positively correlated to 2-AP content following foliar MeJA application. Therefore, our results implied that foliar MeJA application increased aroma and influenced yield by regulating the physio-biochemistry characters and resistance, and suggested that the optimal concentration of MeJA for the best positive effect on the yield and aroma was 1 μM. However, further study is required to evaluate the metabolic level and molecular basis of the regulatory mechanism of foliar MeJA application on 2-AP in fragrant rice.

Metabolomics approach to identify key volatile aromas in Thai colored rice cultivars

In addition to white jasmine rice, Thailand has many native-colored rice varieties with numerous health benefits and the potential to become a global economic crop. However, the chemical characteristics of aromatic substances in native-colored rice are still mostly unknown. This study aimed to identify the key volatile aroma compounds and the biosynthetic pathways possibly involved in their formation in Thai native-colored rice varieties, and thus leading to the search for potential genetic markers for breeding colored rice with better aromatic properties. Twenty-three rice varieties in four categories: aromatic white, aromatic black, non-aromatic black, and non-aromatic red, were investigated (n=10 per variety). Seed husks were removed before the analysis of rice volatile aromas by static headspace gas chromatography-mass spectrometry. Untargeted metabolomics approach was used to discover the key volatile compounds in colored rice. Forty-eight compounds were detected. Thirty-eight of the 48 compounds significantly differed among groups at p<0.05, 28 of which at p<0.0001, with the non-aromatic black and red rice containing much lower content of most volatile constituents than the aromatic black and white rice. Focusing on the aromatic black rice, the samples appeared to contain high level of both compound groups of aldehydes (3-methylbutanal, 2-methylbutanal, 2-methylpropanal, pentanal, hexanal) and alcohols (butane-2,3-diol, pentan-1-ol, hexan-1-ol). Biosynthetically, these distinctive black-rice volatile compounds were proposed to be formed from the metabolic degradation of branched-chain amino acids (L-leucine, L-isoleucine and L-valine) and polyunsaturated fatty acids (linoleic acid and α-linolenic acid), involving the branched-chain aminotransferases and keto-acid decarboxylases and the 9-lipoxygonases and 13-lipoxygeases, respectively. The proposed degradative pathways of amino acids and fatty acids were well agreed with the profiles key volatile compounds detected in the Thai native-colored rice varieties.

Increasing basal nitrogen fertilizer rate improves grain yield, quality and 2-acetyl-1-pyrroline in rice under wheat straw returning

Straw returning plays an essential role in crop yields and the sustainable development of agriculture. However, the effects and mechanisms of nitrogen (N) fertilizer management on grain yield, quality and aroma substance 2-acetyl-1-pyrroline (2-AP) content under wheat straw returning are still unclear. In this field experiment, two japonica rice cultivars were used as materials, wheat straw non-returning (NS) and wheat straw full returning (WS) were designed coupled with two N application ratios, namely basal fertilizer: tiller fertilizer: panicle fertilizer =5:1:4 (local farmers' fertilizer practice, LFP) and 7:1:2 (increasing basal fertilizer rate, IBF) under the total N application rate of 270 kg ha^-1. The effects of the four treatment combinations (NS-LFP, NS-IBF, WS-LFP, WS-IBF) on yield, cooking and eating quality, and 2-AP content in rice were investigated. The two-year (2020, 2021) results showed that: 1) WS-IBF significantly increased the number of panicles and grains per panicle, leading to the increase in grain yield by 6.67%-12.21%, when compared with NS-LFP, NS-IBF and WS-LFP. 2) WS-IBF enhanced the taste value, peak viscosity, breakdown value, the ratio of amylopectin to amylose, and the ratio of glutelin to prolamin while reducing the setback value and amylose content of rice flour. 3) Compared with NS, WS increased the activities of proline dehydrogenase and ornithine transaminase, the synthetic precursors of 2-AP, and finally increased 2-AP content in rice grains. WS-IBF slightly decreased 2-AP content, but there was no significant difference with WS-LFP. The above results indicated that adjusting the N regime and increasing basal N fertilizer rate under wheat straw returning is conducive to improving grain yield, cooking and eating quality, and 2-AP content in rice.

Understanding the impact of nitrogen and sulfur precursors on the aroma of dry fermented sausages

The goal of this study was to confirm and acquire more information about the nitrogen and sulfur compounds existing in the volatile profile of dry fermented sausages from the addition of precursors (proline, ornithine and thiamine), and their role in sausage aroma. To this end, the precursors were added to the formulation of sausages, which were submitted to a fermentation and drying process. The sausage aroma was analyzed by olfactometry technique and Free Choice Profile sensory analysis. The results showed that the addition of precursors impacted the aroma, and reduced the level of oxidation in the final sausages while microbial differences were mainly observed in Orn-sausages. Among the aroma compounds detected only 2-methyl-3-(methylthio)furan verified the effect of thiamine supplementation and the impact on the cured and savoury odours detected in Thia-sausages by Free Choice profile sensory analysis, while no clear effect could be attributed to specific volatile compounds in the nitrogen supplemented sausages.

Profiling of 2-Acetyl-1-Pyrroline and Other Volatile Compounds in Raw and Cooked Rice of Traditional and Improved Varieties of India

Herein, optimized headspace solid phase microextraction with gas chromatography–tandem mass spectrometry (HS-SPME-GC-MS/MS) was used to estimate the 2-acetyl-1-pyrroline (2-AP) in raw and cooked rice samples of ten different traditional and improved varieties. Furthermore, HS-SPME-GC-MS-based volatile profiling was subjected to untargeted analyses to identify major odorants in raw and cooked rice samples, and to understand chemical proximities among volatile profiles. Results showed that 2-AP content was remarkably increased in cooked rice compared to raw. Among the varieties studied, Pusa-1652 (Improved Kala Namak) and Kala Namak-2 were superior in the 2-AP content than Basmati varieties. Additionally, Govind Bhog, Kala Jeera and Jeera-32 had 2-AP content equivalent to or superior to Basmati rice varieties. Altogether, 18 and 22 volatiles were identified in the raw and cooked rice samples studied, respectively. Of these, ethyl butyrate, ethyl 3-methylbutanoate, 2-undecanone, ethyl benzoate, ethyl benzeneacetate, 2-methylnaphthalene, and 1-methylnaphthalene were characteristically detected in the cooked rice. The high amount of 2-ethyl-1-hexanol was uniquely found in raw rice samples, which can be a marker compound for freshly milled rice. Along with 2-AP, butanoic acid and benzoic acid derivatives, phenylethyl alcohol, ethyl 3-hydroxybutyrate, and indole may be responsible for the overall perceived characteristic Basmati-like aroma in cooked rice.

Exploring the Lipids Involved in the Formation of Characteristic Lactones in Japanese Black Cattle

The meat from Japanese Black cattle (Japanese Wagyu) is finely marbled and exhibits a rich and sweet aroma known as Wagyu beef aroma. To clarify the key metabolites involved in the aroma, we analyzed the correlation between lactone and lipid composition in Japanese Black cattle. Using gas chromatography-olfactometry, we identified 39 characteristic odorants of the intermuscular fat. Seven characteristic lactones considered to be involved in Wagyu beef aroma were quantified and compared in the marbled area and intermuscular fat using a stable isotope dilution assay. Among them, γ-hexalactone was the only lactone whose level was significantly higher in the marbled area. To explore the lipid species involved in lactone formation, we analyzed samples with different aroma characteristics. Liquid chromatography-mass spectrometry revealed eight lipid classes and showed significant differences in triacylglycerides (TAGs). To determine the molecular species of TAGs, we performed high-performance liquid chromatography analysis and identified 14 TAG species. However, these analyses showed that seven lactones had a low correlation with the TAGs. However, γ-hexalactone showed a positive correlation with linoleic acid. This study suggests that lipid composition affects the characteristic lactone profile involved in the Wagyu beef aroma.

Identification of volatiles and odor-active compounds of aromatic rice by OSME analysis and SPME/GC-MS

During cooking, aromatic rice has a pleasant and characteristic aroma, a relevant factor to add sale value and attract consumer interest. This work studied the volatile compounds of aromatic rice (IAC 500) aiming at identifying those responsible for the aroma and flavor of the cooked rice. The description of the aromatic notes of the IAC 500 rice was carried out by a trained and selected sensory panel, followed by olfactometry (OSME) and identification by GC-MS of the rice volatile compounds extracted by SPME. A total of 80 volatiles was sensorially perceived and/or detected in the chromatographic effluent, of which 65 were identified, 44 presented some odor, and 36 were odorless. Among the odorous compounds, 15 were not detected by GC-FID or GC-MS. This study confirmed the compound 2-acetyl-1-pyrroline as the impacting volatile compound to the aroma of aromatic rice since it presented a very low percentage of area in the chromatogram and a high odor intensity. Other 43 compounds presented odor in lower intensities, but also contributed to the overall aroma of IAC 500 rice. From the 11 aromatic notes mentioned by the trained panel (cooked vegetable/seed, corn, hominy, green, porridge, popcorn, fresh baked cake/bread, milk, caramel, tapioca flour and flower), eight were related to the volatile compounds responsible for their aroma.

Comparison of the sensory properties of fragrant and non-fragrant rice (Oryza sativa), focusing on the role of the popcorn-like aroma compound 2-acetyl-1-pyrroline

2-Acetyl-1-pyrroline (2-AP) has been widely reported as a key contributor to the popcorn-like aroma of fragrant rice (Oryza sativa). To gain a greater understanding of its contribution to the aroma in both fragrant and non-fragrant rice, sensory profiling was conducted with a trained panel to examine the sensory properties of six boiled rice samples, three fragrant and three non-fragrant varieties. The intensity of the popcorn note as an orthonasal odour, a retronasal flavour and as an after-effect was significantly higher in fragrant rice than in non-fragrant rice. However, panellists could not differentiate these popcorn attributes between the three different fragrant rice varieties. 2-AP was extracted from the boiled rice samples by headspace solid-phase microextraction and quantified by gas chromatography-mass spectrometry. 2-AP was below the limits of quantitation in non-fragrant varieties; however, gas chromatography-olfactometry of samples indicated the presence of 2-AP in both raw fragrant and non-fragrant rice varieties.

Preference mapping of different water-to-rice ratios in cooked aromatic white jasmine rice

The volume of water is a key variable affecting texture and flavor attributes of cooked rice with a significant influence on consumer preference. The aim of this study was to determine the attributes driving consumer preference for rice cooked with different water-to-rice ratios. Descriptive analysis (DA) methodology was employed to profile aromatic white Jasmine rice and a consumer study was run to determine preference for water-to-rice ratios. A DA panel (n = 12) evaluated ten aroma, four taste and flavor, three texture, and six appearance attributes for aromatic white Jasmine rice cooked with four water-to-rice ratios (1.125:1, 1.5:1, 1.875:1, and 2.25:1). Rice consumers (n = 117) evaluated preferences of the same aromatic white Jasmine rice cooked with the aforementioned water-to-rice ratios. DA results revealed floral aroma, firmness, chewiness, coarseness, stickiness/cohesiveness, and fluffiness were significantly influenced by an increasing water-to-rice ratio. There was no significant effect of water-to-rice ratios on consumer preferences (χ² (3, 117) = 1.17; P = 0.76). Consumers were grouped into three clusters with similar preference patterns using agglomerative hierarchical clustering. External preference mapping techniques run on each consumer cluster determined the water-to-rice ratios 1.125:1 and 1.875:1 as having the largest appeal to heavy consumers of rice, split by preferences for fluffy or sticky cooked rice. The water-to-rice ratio 1.5:1 was not dominated by any single attribute or group of attributes, appealing to less frequent rice consumers. Therefore, the water-to-rice ratios 1.125:1, 1.5:1, and 1.875:1 should satisfy the broadest groups of Australian rice consumers. PRACTICAL APPLICATION: Rice, a high volume commodity can be cooked using a variety of methods and volumes of water. The findings of this research will help manufacturers market water-to-rice ratios, assisting consumers in identifying cooked rice for which they have a preference.

Characterization of the Key Aroma Compounds in Traditional Hunan Smoke-Cured Pork Leg (Larou, THSL) by Aroma Extract Dilution Analysis (AEDA), Odor Activity Value (OAV), and Sensory Evaluation Experiments

The key aroma compounds in smoke-cured pork leg were characterized by gas chromatography-olfactometry coupled with aroma extract dilution analysis (GC-O/AEDA), odor activity value (OAV), recombination modeling, and omission tests. Ranking analysis showed that pork leg smoke-cured for 18 days had the best sensory qualities, with strong meaty, smoky, roasty, woody, and greasy attributes. Thirty-nine aroma-active regions with flavor dilution (FD) factors ranging from 9 to 6561 were detected. Overall, 3-ethylphenol had the highest FD factor of 6561, followed by 2,6-dimethoxyphenol, 3,4-dimethylphenol, 4-ethylguaiacol, 4-methylguaiacol, 3-methylphenol, and 2-acetyl-1-pyrroline, with FD ≥243. Among 39 aroma compounds, 27 compounds with OAVs ≥1 and were potent odorants. A similarity of 90.73% between the recombination model and traditional Hunan Smoke-cured Pork Leg (THSL) sample was obtained. Omission tests further confirmed that (E)-2-nonenal, 2-methoxy-4-vinylphenol, guaiacol, 3-ethylphenol, 2,6-dimethylphenol, 2-acetyl-1-pyrroline, and methional were key odorants in smoke-cured pork leg. Additionally, 2-acetyl-1-pyrroline (38.88 μg/kg), which contributes to a roasty aroma, was characterized here as a key odorant of smoke-cured pork leg for the first time.

Nitrogen application and different water regimes at booting stage improved yield and 2-acetyl-1-pyrroline (2AP) formation in fragrant rice

BACKGROUND

Water (W) and nitrogen (N) management generally cause regulations in the 2-acetyl-1-pyrroline (2AP) accumulation in fragrant rice; nevertheless, the feasibility of such management strategies at booting stage in improving 2AP accumulation has not been examined in details.

METHODS

Field experiments were conducted in the early season (March-July) and repeated in the late season (July-November) in 2013. The treatments were applied urea (90 kg ha^- 1), calcium super phosphate (90 kg ha^- 1) and potassium chloride (195 kg ha^- 1) as basal fertilizer, and urea (65 kg ha^- 1) at tillering stage. Three N levels i.e., 0 kg N ha^- 1 (N1), 30 kg N ha^- 1 (N2), and 60 kg N ha^- 1 (N3) and three water levels i.e., W1 treatment (well-watered treatment with water layer of 2-4 cm), W2 treatment (soil water potential was - 15 ± 5 kPa), and W3 treatment (soil water potential was - 25 ± 5 kPa) at booting stage was set up for three rice varieties i.e., Nongxiang 18, Yungengyou 14 and Basmati. The grain yield, head milled rice yield, 2AP contents and the biochemical parameters related to 2AP formation were investigated.

RESULTS

Result indicated that W and N dynamics regulated the grain yield, head milled rice yield, and 2AP contents in brown rice across three varieties. The N2 and N3 treatment significantly increased the 2AP contents in brown rice by 9.54% and 11.95%, and 8.88% and 32.54% in the early and the late season, respectively; improved grain yield and head milled rice yield. The W3 treatment improved grain yield, head milled rice yield and 2AP content. Significant W and N interaction effect on 2AP content in brown rice was detected, where the W3 N3 treatment showed the strongest interaction regarding improvement of 2AP contents in brown rice. The 2AP accumulation and its related biochemical parameters and their relationships in different plant tissues at different growth stages under W and N treatments had also been assessed. The 2AP content, P5C content and DAO activity during grain filling periods was highly related to the 2AP content in brown rice.

CONCLUSION

This study revealed that the 60 kg N ha^- 1 coupled with - 25 ± 5 kPa treatment showed the best positive effects on yield and aroma in fragrant rice, suggested that water and nitrogen management at booting stage can improve grain yield and fragrance in fragrant rice. However, further study to evaluate the metabolic and molecular basis of 2AP accumulation in fragrant rice is needed.

Quantitation of 2-acetyl-1-pyrroline in aseptic-packaged cooked fragrant rice by HS-SPME/GC-MS

Aseptic-packaged cooked rice (APCR) is a rice-based food product with a rapidly increasing market size, and APCR made of fragrant rice (FR) has recently appeared on the market. The fragrance of FR is produced by a combination of odoriferous compounds, among which 2-acetyl-1-pyrroline (2AP) has been identified as the most important contributor to overall aroma. This study describes the development of a method to quantify 2AP in FR-based APCR using headspace solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS). The recovery of 2AP spiked into APCR was lower than 10%, which suggests significant matrix effects and inappropriateness of external standard-based calibration. For standard addition calibration method, up to 1,000 ng of 2AP were spiked into APCR containing 0% to 100% FR. Subsequent regression analyses of recovered peak area (Y) as a function of the amount of 2AP spiked (X) yielded highly linear calibration curves (R 2 > 0.9917) with consistent slopes (RSD = 2.7%), regardless of FR composition. Y-intercepts, however, which represent the amount of 2AP in APCR without spiking, increased linearly (R 2 = 0.9898) in proportion to the composition of FR in the APCR. The amount of 2AP in APCR, determined by extrapolating the standard addition calibration curves, also increased linearly (R 2 = 0.9963) as a function of FR composition. Practicality of developed method was tested by monitoring 2AP contents in APCR under realistic storage conditions, which successfully demonstrated 38% and 60% 2AP reductions in APCR of 20% FR after 1 and 2 months of storage at 25°C, respectively. The present study demonstrates that a standard addition method, whereby up to 1,000 ng of 2AP standard is spiked into 4 g of APCR containing 5%-100% FR in a 20-mL headspace vial followed by SPME/GC-MS, may serve as an effective means of quantitating 2AP in fragrant rice-based APCR.

Effects of milling on aromatics, lipophilic phytonutrients, and fatty acids in unprocessed white rice of scented rice 'Cheonjihyang-1-se

To understand effects of milling, scented rice 'Cheonjihyang-1-se' was milled from 10 to 140 s and changes in volatiles, phytonutrients, and fatty acids were evaluated. Among 43 identified odor-active compounds, four volatiles, including hexan-3-one, exhibited decreases of up to 78%, while four others including (E)-non-2-enal, increased following milling. Levels of 2-acetyl-1-pyrroline, the most distinctive popcorn-flavoring compound in scented rice, were not affected by the degree of milling (DM). Partial least squares discriminant analyses of volatiles were able to differentiate white rice according to the DM. Benzene and 2-pentylfuran showed the highest variable importance in projection scores, which could be applied in estimating the DM of rice. Milling significantly decreased tocopherols, tocotrienols, squalene, phytosterols contents and oleic acid composition, while palmitic acid composition was increased. These results suggest milling-dependent variations in phytonutrient levels and lipid composition, as well as changes in aroma and subsequent market quality, in 'Cheonjihyang-1-se' rice.

Aged (Black) versus Raw Garlic against Ischemia/Reperfusion-Induced Cardiac Complications

Recent evidence from studies suggests that aged black garlic also has an effect on health. The major aim of the present study is to compare the effect of raw and aged black garlic on postischemic cardiac recovery. Male Sprague Dawley rats were randomly divided into three groups. Animals of the first group were fed with raw garlic, animals of the second group received aged black garlic, while the third group served as vehicle-treated controls. Upon conclusion of the treatment, isolated hearts were undertaken to ischemia/reperfusion. Heart function and infarct size were measured and the level of HO-1 and iNOS were studied. Superior postischemic cardiac function and reduced infarct size in both garlic treated groups compared to the drug-free control group, indicated cardioprotective effects. However, no significant differences between the garlic treated groups were observed. Western blot analysis revealed that raw garlic enhanced the level of HO-1 before ischemia, while in ischemic samples, we found elevated HO-1 expression in both garlic treated groups. The level of iNOS was the same before ischemia in all groups, however, a markedly reduced iNOS level in ischemic/reperfused hearts originating from control and raw garlic treated animals was observed. Samples from aged black garlic treated animals demonstrated that the level of iNOS was not significantly reduced after ischemia/reperfusion. Taken together these results indicate that not only raw but also aged black garlic possess a cardioprotective effect.