Aroma-active compounds of wild rice (Zizania palustris L.)

Effects of pan- and air fryer-roasting on volatile and umami compounds and antioxidant activity of dried laver (Porphyra dentata)

This study aimed to investigate the impact of pan- and air fryer-roasting on the volatiles, umami compounds, antioxidant activity, and sensory attributes of dried laver (Porphyra dentata). To assess the influence of time and temperature, pan-roasting was conducted at temperatures of 250, 300, and 350 °C for 5, 10, and 15 s, respectively. For air fryer-roasting, dried laver was roasted at 160, 170, and 180 °C for 2, 4, and 6 min, respectively. In both roasting methods, the levels of 1,5-octadien-3-ol and 1-octen-3-ol significantly decreased (p < 0.05) with increased time and temperature. The Equivalent Umami Concentration ranged from 94.89 to 518.09 g MSG/100 g. The antioxidant activity significantly increased (p < 0.05) with higher roasting temperatures and longer durations, whereas pigment content significantly decreased. The browning index increased by 64% and 43% for the pan and air frying methods, respectively. The samples pan-roasted at 300 °C for 15 s obtained the highest sensory scores.

Sensory improvement and antioxidant enhancement in silver carp hydrolysate using prebiotic oligosaccharides: insights from the Maillard reaction

Our previous studies have highlighted the potential of silver carp hydrolysate (SCH) in managing chronic diseases. Unfortunately, its fishy smell and bitter taste limited consumer acceptance. Prebiotic oligosaccharides are often used as dietary supplements, ignoring their role as carbonyl ligands in the Maillard reaction to enhance food's sensory and antioxidant properties. This study aimed to improve SCH's sensory attributes and investigate its physicochemical properties and antioxidant activities using prebiotic oligosaccharides via the Maillard reaction. The results showed that xylo-oligosaccharide (XOS) had the highest reactivity among the oligosaccharides tested, and it greatly enhanced the taste and flavor of SCH, as well as its antioxidant activities (0.45 to 16.5 times). Specifically, XOS effectively reduced the fishy smell and bitter taste, imparting a caramel-like flavor and overall acceptability to SCH. The improved flavor profile was attributed to the increased presence of sulfur-containing and nitrogen oxide volatile flavor compounds, such as benzothiazole, methional, and furans, which also contributed to antioxidant effects. Sensory evaluation results indicated that SCH obtained from papain exhibited a stronger bitter taste than that obtained from alcalase. Additionally, XOS imparted a reddish-brown color to SCH due to the higher browning intensity. This study is the first to demonstrate that XOS in the Maillard reaction can effectively improve the undesirable flavor and taste of SCH while enhancing its antioxidant activities, providing a theoretical basis for developing SCH as a market-acceptable functional food ingredient.

Analysis of rice characteristic volatiles and their influence on rice aroma

Rice aroma, one of the most important qualities of rice, was the comprehensive result of volatiles in rice and human sense. In this study, the main volatile compounds in rice were analyzed by using gas chromatography-mass spectrometry and gas chromatography-olfactometry, and their correlations with sensory score were investigated. A total of eighty-five volatiles were found in rice samples. By combining odor activity value and correlation analysis, nine volatiles were considered as potential characteristic volatiles in rice aroma, namely hexanal, 2-pentylfuran, octanal, 2-acetyl-1-pyrroline (2-AP), 1-octen-3-ol, trans-2-octenal, decanal, trans-2-nonenal and trans, trans-2,4-decadienal. It was found that the volatiles negatively correlated with sensory scores were positively correlated with hexanal. It indicated that hexanal might be a representative of the negative volatiles of rice aroma. The effects of the nine potential characteristic volatiles on rice aroma were investigated by using sensory analysis. The results showed that the odor intensity and preference level of 2-AP, hexanal, and 1-octen-3-ol were significantly affected by the content. Furthermore, the aroma of cooked rice was significantly different after adding 2-AP, hexanal or trans, trans-2,4-decadienal. Rice aroma was increased by adding 2-AP and deteriorated by adding hexanal or trans, trans-2,4-decadienal, indicating that 2-AP contributed positively to rice aroma while hexanal and trans, trans-2,4-decadienal contributed negatively to rice aroma. Hexanal, 2-AP, and trans, trans-2,4-decadienal were suggested to be the key characteristic volatiles for future aroma evaluation.

Precise Authenticity of Quinoa, Coix Seed, Wild Rice and Chickpea Components Using Optimized TaqMan Real-Time PCR

Functional food such as, quinoa, coix seed, wild rice and chickpea have experienced rapidly increasing demand globally and exhibit high economic values. Nevertheless, a method for rapid yet accurate detection of these source components is absent, making it difficult to identify commercially available food with labels indicating the presence of relevant components. In this study, we constructed a real-time quantitative polymerase chain reaction (qPCR) method for rapid detection of quinoa, coix seed, wild rice and chickpea in food to identify the authenticity of such food. Specific primers and probes were designed with 2S albumin genes of quinoa, SAD genes of coix seed, ITS genes of wild rice and CIA-2 genes of chickpea as the target genes. The qPCR method could specifically identify the four wild rice strains, yielding, LODs of 0.96, 1.14, 1.04 and 0.97 pg/µL quinoa, coix seed, wild rice and chickpea source components, respectively. Particularly, the method allowed the identification of the target component with content below 0.01%. A total of 24 commercially available food samples of different types were detected by using the method and the results indicate that the developed method is applicable to the detection of different food matrices, as well as authenticity verification in deeply processed food.

Flavor properties of Chinese noodles processed by dielectric drying

Volatile organic compounds (VOCs) significantly impact food flavor. In this work, Electron nose (E-nose), head space solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), and head space-gas chromatography-ion mobility spectrometry (HS-GC-IMS) techniques were applied to analyze different drying effects: microwave, hot air, and radio frequency on the aroma of Chinese noodles. E-nose analysis suggests that aromatic differences are mainly from broad range-methane. HS-SPME-GC-MS and HS-GC-IMS identified 47 and 26 VOCs in the fresh and dried noodles, respectively. The VOCs in the dried noodles were mainly aldehydes, alcohols, and esters. Drying significantly reduced the types of VOCs in Chinese dried noodles. Microwave dried noodles exhibited the strongest aroma after the shortest time of treatment, suggesting microwave drying may be the best drying method for noodles. Using aromatic analysis, this paper provides useful information for understanding the flavor of flour products and offers new ideas for drying noodles.

Development of Gluten-Free Rice Flour Noodles That Suit the Tastes of Japanese People

Gluten-free rice flour noodles with a flavor and texture profile preferred by the Japanese people were developed. The rice noodles contained potato starch (PS) as a binder. “Koshihikari” was selected from several candidate varieties based on its pasting properties. Since the Japanese people prefer the chewy texture of wheat flour “Udon” noodles, first, the stress−strain characteristics of “Udon” noodles in Japan were quantified, using a mechanical test. Next, different formulations of rice noodles were prepared by changing the amount of PS blended into the noodles. The mechanical tests on wheat and rice noodles show that rice noodles made from 85% rice flour and 15% PS have a texture similar to that of “Udon” noodles. Brown rice noodles containing roasted brown rice flour were also developed. Since brown rice flour hinders the binding of the dough, it was necessary to increase the amount of PS to increase the binding of roasted brown rice flour. Finally, noodles with 70% white rice flour, 10% brown rice flour, and 20% PS were produced. The gas chromatography−mass spectrometry analysis of the volatile compounds contained in white rice noodles and brown rice noodles identified the volatile compounds characteristic each of type.

Identification and Functional Analysis of Glutathione S-Transferases from Sitophilus zeamais in Olfactory Organ

Simple Summary

Sitophilus zeamais is a worldwide pest that destroys many grain products, causing a loss of cereal quality and quantity resulting from its metabolites and behavior. Glutathione S-transferases (GSTs), as a group of odorant-degrading enzymes (ODEs), play an important role in degrading xenobiotic odorant molecules in insect olfactory sensing systems. However, there have been few reports about the function of the GST genes of S. zeamais in the odorant-degrading process. In this study, we characterized 13 full-length genes encoding GST sequences from S. zeamais and analyzed the expression pattern in different tissues of SzeaGSTd1. In addition, we investigated the ability of recombinant SzeaGSTd1 to degrade the volatile molecules of the host, and the data indicated that the content of capryl alcohol significantly decreased in the system. In summary, we believe SzeaGSTd1 plays a key role in the olfactory sensing system of S. zeamais.

Abstract

Odorant-degrading enzymes (ODEs) play an important role in rapidly degrading and inactivating odorant molecules that have completed information transmission, as well as in maintaining the stability and sensitivity of insect olfactory sensing systems. Glutathione S-transferases (GSTs), as a group of ODEs, supposedly bear the ability to catalyze the conjugation of glutathione (GSH) and xenobiotic odorant molecules in the degrading process. However, there are few reports regarding the role of the GST genes of Sitophilus zeamais in the degrading process. Thus, we characterized 13 full-length genes encoding GST sequences from S. zeamais, of which only SzeaGSTd1 contained a high abundance in the antennae. Ligand-binding assays implied that SzeaGSTd1 was able to catalyze the conjugation of GSH with 2, 4-dinitrochlorobenzene (CDNB). We investigated whether recombinant SzeaGSTd1 bears the ability to degrade the volatile molecules of the host; among the host volatiles, and found capryl alcohol to be a suitable substrate for SzeaGSTd1. These results strongly suggest that SzeaGSTd1 probably plays a role in auxiliary host location by degrading the host volatiles of capryl alcohol and exhibits a potential biological function in the olfactory sensing system of S. zeamais. Knowledge of the potential functions of SzeaGSTd1 will provide new ideas for biological control strategies for S. zeamais.

Identification of Key Volatiles Differentiating Aromatic Rice Cultivars Using an Untargeted Metabolomics Approach

Non-aromatic rice is often sold at the price of aromatic rice to increase profits, seriously impairing consumer experience and brand credibility. The assessment of rice varieties origins in terms of their aroma traits is of great interest to protect consumers from fraud. To address this issue, the study identified differentially abundant metabolites between non-aromatic rice varieties and each of the three most popular aromatic rice varieties in the market using an untargeted metabolomics approach. The 656 metabolites of five rice grain varieties were determined by headspace solid-phase extraction gas chromatography-mass spectrometry, and the multivariate analyses were used to identify differences in metabolites among rice varieties. The metabolites most differentially abundant between Daohuaxiang 2 and non-aromatic rice included 2-acetyl-1-pyrroline and acetoin; the metabolites most differentially abundant between Meixiangzhan 2 and non-aromatic rice included acetoin and 2-methyloctylbenzene,; and the metabolites most differentially abundant between Yexiangyoulisi and non-aromatic rice included bicyclo[4.4.0]dec,1-ene-2-isopropyl-5-methyl-9-methylene and 2-methylfuran. Overall, acetoin was the metabolite that was most differentially abundant between the aromatic and non-aromatic rice. This study provides direct evidence of the outstanding advantages of aromatic rice and acts a reference for future rice authentication processes in the marketplace.

Discrimination of rice varieties using smartphone-based colorimetric sensor arrays and gas chromatography techniques

A smartphone-based colorimetric sensor array system was established for discrimination of rice varieties having different geographical origins. Purposely, aroma profiling of nine rice varieties was performed using solid-phase microextraction gas chromatography-mass spectrometry. Alcohols, aldehydes, alkanes, ketones, heterocyclic compounds, and organic acids represent the abundant compounds. Colorimetric sensor array system produced a characteristic color difference map upon its exposure to volatile compounds of rice. Discrimination of rice varieties was subsequently achieved using principal component analysis, hierarchical clustering analysis, and k-nearest neighbors. Rice varieties from same geographical source were clustered together in the scatter plot of principal component analysis and hierarchical clustering analysis dendrogram. The k-nearest neighbors algorithm delivered optimal results with discrimination rate of 100% for both calibration and prediction sets using sensor array system. The smartphone-based colorimetric sensor array system and gas chromatography technique were able to effectively differentiate rice varieties with the advantage of being simple, rapid, and low-cost.

Sensory and Chemical Characteristic of Two Insect Species: Tenebrio molitor and Zophobas morio Larvae Affected by Roasting Processes

The volatile compounds from insects (Tenebrio molitor and Zophobas morio larvae) roasted at 160, 180, or 200 °C and fed with potato starch or blue corn flour were isolated by solid-phase microextraction (SPME), and identified by gas chromatography-mass spectrometry (GC-MS). In the tested material, 48 volatile compounds were determined. Among them, eight are pyrazines, aroma compounds that are formed in food products during thermal processing due to the Maillard reaction. Eleven of the identified compounds influenced the roast, bread, fat, and burnt aromas that are characteristic for traditional baked dishes (meat, potatoes, bread). Most of them are carbonyl compounds and pyrazines. To confirm the contribution of the most important odorants identified, their odor potential activity values (OAVs) and %OAV were calculated. The highest value was noted for isobuthylpyrazine, responsible for roast aroma (%OAV > 90% for samples roasted at lower temperatures), and 2,5-dimethylpyrazine, responsible for burnt aroma (%OAV > 20% for samples roasted at the highest temperature). According to the study, the type of feed did not significantly affect the results of the sensory analysis of roasted insects. The decisive influence was the roasting temperature. The highest scores were achieved for Tenebrio molitor larvae heat-treated at 160 °C.

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.

Changes in flavor of fragrant rice during storage under different conditions

BACKGROUND

Because of its high nutritional value and good sensory properties, fragrant rice is very popular all over the world. The aroma and taste of fragrant rice play an essential role in its sensory properties. However, there has been a lack of studies on flavor changes in fragrant rice during storage.

RESULTS

Hexanal, nonanal, benzaldehyde, hexadecanoic acid, and methyl ester, were identified as aroma-active compounds in fresh fragrant rice. After storage, more than 100 volatile compounds can be identified. The results indicated that, at high-temperature storage, volatile compounds such as aldehydes, ketones, and furans increased, which led to a deterioration in rice quality. Marker compounds of flavor deterioration, methyl palmitate, 2-methyl-propanoic acid, and 3-hydroxy-2,2,4-trimethylpentyl ester, were determined by principal component analysis. In addition to threonine and proline, the other 14 amino acids contributed to the taste of fragrant rice during storage. Sucrose is the only main contributor to the sweetness of Daohuaxiang 2, whereas glucose and fructose had a little sweet taste contribution during storage. The electronic nose (e-nose) and the electronic tongue (e-tongue) could distinguish samples with different storage conditions.

CONCLUSION

Different storage conditions can cause flavor differences in fragrant rice. Especially under high-temperature storage, volatile compounds such as aldehydes, ketones, and furans increase, which is an important reason for the deterioration in the quality of fragrant rice during storage. © 2020 Society of Chemical Industry.

Characterization of the Expression and Functions of Two Odorant-Binding Proteins of Sitophilus zeamais Motschulsky (Coleoptera: Curculionoidea)

Odorant-binding proteins (OBPs) are important in insect chemical communication. The objective of this research was to identify the functions of two OBPs in Sitophilus zeamais. qRT-PCR and western blot (WB) were performed to investigate the expression profiles at the transcript and protein levels, respectively. Fluorescence competitive binding assays were used to measure the ability of the OBPs to bind to host volatiles, and a Y-tube olfactometer was used to verify the results (attraction/no response) via behavioral experiments. The RNAi was used to verify the function by knocking down the ability of proteins to bind odorants. qRT-PCR showed the highest expression SzeaOBP1 and SzeaOBP28 at the low-instar larva (LL) and eclosion adult (EA) stages, respectively. WB showed that both SzeaOBP1 and SzeaOBP28 were highly expressed in the EA stage. Fluorescence competitive binding assays indicated that SzeaOBP1 exhibited extremely high binding affinity with cetanol. SzeaOBP28 exhibited a pronounced binding affinity for 4-hydroxy-3-methoxybenzaldehyde. The behavioral experiment showed that the adult S. zeamais responded strongly to 4-hydroxy-3-methoxybenzaldehyde and valeraldehyde from Sorghum bicolor. The RNAi knockdown individuals displayed behavioral differences between normal insects and dsRNA (SzeaOBP1)-treated insects. We infer that they both have functions in perception and recognition of host volatiles, whereas SzeaOBP28 may also have other functions.

Aroma profile of rice varieties by a novel SPME method able to maximize 2-acetyl-1-pyrroline and minimize hexanal extraction

The solid phase microextraction (SPME) has been the most used technique for the extraction of volatile compounds from rice because of its easy operation and solvent-free. The extraction parameters, sample mass and incubation temperature, were optimized through a central composite rotational design (CCRD), aiming at maximizing the extraction of 2-acetyl-1-pyrroline (2AP), the main compound responsible for the aroma in aromatic rice, and minimizing the generation of hexanal, a marker of lipid oxidation. Besides, the time of sample incubation and fiber exposure for the extraction of the volatile compounds from rice were determined. The optimized conditions for SPME were: 2.5 g of ground rice in a 20 mL vial, sample incubation at 80 °C for 60 min and exposure of the divinylbenzene/carboxene/polydimethylsiloxane (DVB/CAR/PDMS) fiber in the headspace for 10 min. The optimized method was sucessfuly applied to 12 varieties of rice and principal component analysis (PCA) was performed to observe similarities in their volatile profile. A total of 152 volatile compounds were identified among the different rice varieties. From these, 42 were identified in arborio rice, 47 in basmati brand A, 43 in basmati brand B, 55 in black rice, 63 in brown rice, 39 in jamine rice, 50 in parboiled brown rice, 43 in parboiled rice, 54 in red rice, 63 in sasanishiki rice, 46 in white rice and 70 in wild rice.

HPLC Separation of 2-Ethyl-5(6)-methylpyrazine and Its Electroantennogram and Alarm Activities on Fire Ants (Solenopsis invicta Buren)

2-Ethyl-3,6-dimethylpyrazine (EDMP) was an alarm pheromone component isolated from the mandibular gland of the red imported fire ant, Solenopsis invicta Buren. Several pyrazine analogues have been previously found to elicit significant alarm responses in S. invicta workers. This study aimed to separate the commercially available 2-ethyl-5(6)-methylpyrazine (EMP), i.e., a mixture of 2-ethyl-6-methylpyrazine (2E6MP) and 2-ethyl-5-methylpyrazine (2E5MP), and to examine both electroantennogram (EAG) and behavioral responses of S. invicta workers to EMP and the purified isomers. HPLC separations were achieved using a polysaccharide chiral stationary phase (Chiralpak AD-H) column with both mobile phases: Cyclohexane/isopropanol, and hexane/isopropanol. A ratio of 99:1 was selected for the separation of EMP at semipreparative level. The structures of the isomers obtained through the cyclohexane/isopropanol mobile phase were confirmed by detailed analyses of 2D-HSQC- and -HMBC-NMR data. The two isomers showed differential methine C⁻H correlations evidenced by 2D-HMBC-NMR spectra. The two concentrated fractions obtained through hexane/isopropanol mobile phase were subjected to EAG test and behavioral bioassay on S. invicta workers. The two HPLC−purified isomers, 2E6MP and 2E5MP, and their mixture (1:1) at same dose elicited similar EAG and alarm responses, indicating that these two isomers are equally active. The 2D-NMR−spectroscopic characterization, and electrophysiological and alarm activities of 2E6MP and 2E5MP were reported here for the first time.

Analysis of volatiles in brown rice, germinated brown rice, and selenised germinated brown rice during storage at different vacuum levels

BACKGROUND

The quality of nutritionally enhanced foods can be determined by evaluating changes in the volatile compounds produced in these foods over time. In this work, selenium-enriched germinated brown rice (Se-GBR), germinated brown rice (GBR), and brown rice (BR) stored under 90% relative humidity, 38 °C, and various vacuum levels were investigated. The relative abundance and differences of volatile compounds in Se-GBR, GBR, and BR over various storage periods were detected. The correlation of volatile compound abundance with vacuum level and storage time was analysed using principal component analysis (PCA).

RESULTS

Volatile compounds in the three samples were quantified at various storage periods (0, 90 and 150 days). Approximately 100 volatile compounds and eight species were identified and classified. Various proportions or types of volatile compounds were found in each sample at different sampling times. PCA results showed an isolation of volatile compounds in terms of sampling day and vacuum level at each storage period.

CONCLUSION

Changes in volatile compounds over time and vacuum levels can provide bases for assessing of the nutritional quality of Se-GBR, GBR, and BR. © 2017 Society of Chemical Industry.

Quality evaluation, fatty acid analysis and untargeted profiling of volatiles in Cambodian rice

This study provides the first investigation of the physical traits, pasting properties and volatile compounds of Cambodian rice cultivars, including traditional, improved, and improved traditional varieties, allowing for their differentiation as high and low quality rice. Analysis of the grain quality traits illustrates interesting features of traditional varieties and correlations between traits that assist with understanding texture. Untargeted profiling of volatile compounds shows that high quality fragrant varieties not only contain 2-acetyl-1-pyrroline but also several other compounds, including aldehydes, alcohols and 2-alkylfurans that contribute to overall aroma. Moreover, low odour threshold volatile compounds, which can be derived from the oxidation of unsaturated fatty acids, were more abundant in the fragrant varieties. The percentage area of both oleic and linoleic acid were found to be significantly different among the rice varieties tested. Such findings suggest that unsaturated fatty acids in milled rice contribute to rice fragrance, and thereby to overall quality.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation and fate: an example of the coordinate contribution of lipid oxidation and Maillard reaction to the production and elimination of processing-related food toxicants

Major chemical reactions dealing with carbonyl chemistry in foods (Maillard reaction and lipid oxidation) play a role in PhIP formation and fate, pointing to this and analogous heterocyclic aromatic amines as outcomes of this chemistry.