Flavor lexicon for sensory descriptive profiling of different rice types

Systematical construction of rice flavor types based on HS-SPME-GC-MS and sensory evaluation

Rice is one of the main staple foods of Chinese people and its quality requirements are also improving. Aroma is one of the evaluation factors of rice quality, rice with better aroma quality is often more accepted by consumers. A universal aroma descriptive lexicon was established and four flavor types were formed based on samples from 9 representative rice cultivation regions. The key variables affecting the sensory quality of Chinese rice flavor were screened. It was found that the hexanal and nonanal with the highest content had no effect on the flavor properties, which suggests that volatile organic compounds (VOCs) content is not necessarily related to the influence of flavor properties. According to the aroma analysis of different rice flavor types, it can provide guidance for other flavor research.

Characteristic Flavor Compounds and Functional Components of Fragrant Rice with Different Flavor Types

Fragrant rice has various flavor types, mainly the popcorn flavor, corn flavor and lotus root flavor. Chinese fragrant rice from China and Thai fragrant rice from Thailand were analyzed. GC-MS was used to determine the volatile compounds of fragrant rice. It was found that there were 28 identical volatile compounds between Chinese and Thai fragrant rice. The key compounds of different flavor types of fragrant rice were obtained by comparing the common volatile compounds. The key compounds of the popcorn flavor were 2-butyl-2-octenal, 4-methylbenzaldehyde, ethyl 4-(ethyloxy)-2-oxobut-3-enoate and methoxy-phenyl-oxime. The key compounds of the corn flavor were 2,2',5,5'-tetramethyl-1,1'-biphenyl, 1-hexadecanol, 5-ethylcyclopent-1-enecarboxaldehyde and cis-muurola-4(14), 5-diene. By using a combination of GC-MS and GC-O, the flavor spectrogram of fragrant rice was constructed, and the characteristic flavor compounds of each flavor type were identified. It was found that the characteristic flavor compounds of the popcorn flavor were 2-butyl-2-octenal, 2-pentadecanone, 2-acetyl-1-pyrroline, 4-methylbenzaldehyde, 6,10,14-trimethyl-2-pentadecanone, phenol and methoxy-phenyl-oxime. The characteristic flavor compounds of the corn flavor were 1-octen-3-ol, 2-acetyl-1-pyrroline, 3-methylbutyl 2-ethylhexanoate, methylcarbamate, phenol, nonanal and cis-muurola-4(14), 5-diene. The characteristic flavor compounds of the lotus root flavor were 2-acetyl-1-pyrroline, 10-undecenal, 1-nonanol, 1-undecanol, phytol and 6,10,14-trimethyl-2-pentadecanone. The resistant starch content of lotus root flavor rice was relatively high (0.8%). The correlation between flavor volatiles and functional components was analyzed. It was found that the fat acidity of fragrant rice was highly correlated (R = 0.86) with the characteristic flavor compounds, such as 1-octen-3-ol, 2-butyl-2-octenal and 3-methylbutyl-2-ethylhexanoate. The characteristic flavor compounds had an interactive contribution to the production of the different flavor types of fragrant rice.

Impact of Monascus purpureus fermentation on antioxidant activity, free amino acid profiles and flavor properties of kelp (Saccharina japonica)

This study evaluated the efficacy of Monascus purpureus fermentation on Saccharina japonica (SJ). Healthy substances and antioxidant activity of fermented SJ (FSJ) were determined. Results showed that fermentation caused the release of phenolic compounds and flavonoids, which resulted in the enhancement of antioxidant activity. Essential amino acids and γ-aminobutyric acid also greatly accumulated in FSJ. Sensory evaluation and gas chromatography-ion mobility spectrometry (GC-IMS) were used to evaluate flavor properties of FSJ. A lexicon consisted of 24 descriptors was established for SJ and FSJ, of which 14 descriptors were regarded as odor attributes. A total of 46 volatile compounds were identified by GC-IMS and showed positive correlation with odor attributes. Fifteen volatile compounds were screened as key compounds, tricarboxylic acid cycle, embden-meyerhof-parnas and amino acid catabolism were main formation metabolisms of them. Advanced properties of FSJ indicated that fermentation is a promising approach for the production of SJ food.

On-farm comparison in grain quality between main and ratoon crops of ratoon rice in Hubei Province, Central China

BACKGROUND

While ratoon rice has been increasingly practiced by farmers recently in China, on-farm performance in grain quality of main and ratoon crops in the mechanized rice ratooning system is less studied and remains poorly understood. Therefore, a multi-location on-farm survey was conducted to collect rice grain samples from farmers' fields to determine grain quality of main and ratoon crops of ratoon rice at 12 locations across Hubei Province, central China, in 2016.

RESULTS

On average, milled and head rice percentage in the ratoon crop was 70.2% and 65.7%, which was significantly higher than in the main crop, whereas chalky grain percentage and grain chalkiness in ratoon crop (10.1% and 2.8%, respectively) were significantly lower than those in the main crop (36.6% and 14.2%, respectively). The differences in these quality traits between the two crops were consistent at all locations. Averaged across 12 locations, scores of translucency and gel consistency were significantly lower but amylose content and alkali spreading value were significantly higher in the ratoon crop than in the main crop, with the difference between the two crops varying in gel consistency by location.

CONCLUSION

Overall, grain quality, especially milling and appearance of the ratoon crop, was superior to the main crop in the mechanized rice ratooning system. As a result, this study emphasizes the potential role of the rice ratooning system in other regions with a similar biophysical background producing high-quality rice. © 2022 Society of Chemical Industry.

Volatile Organic Compounds, Evaluation Methods and Processing Properties for Cooked Rice Flavor

Rice (Oryza sativa L.), as the main refined grain in China, has attracted much attention in terms of quality. Rice is usually consumed after cooking, and it is a commonly staple food. Nowdays, people's requirements for cooked rice focus more on the taste characteristics and quality. Furthermore, aroma is one of the primary sensory reference points, which is the most intuitive way for people to judge cooked rice. By integrating and analyzing the researches of cooked rice aroma identification in recent five years, this paper expounds the extraction and identification methods (sensory evaluation method, GC-MS, SPME, MOS sensors, electronic nose, etc.) of the flavor substances in cooked rice, as the processing methods and properties of cooked rice, and the volatile organic compounds of cooked rice under different conditions are summarized as well.

HS-GC-IMS identification of volatile aromatic compounds of freshly-cooked rice packaged with different disposable lunchboxes

The rapid development of online-to-offline food delivery service has necessitated the replacement of plastic lunchbox using biodegradable ones. In current study, a total number of fourteen panelists were firstly recruited and trained to investigate how different commercial disposable lunchboxes affect the freshly cooked rice sensory properties during heat preservation (60 °C, 60 min). The lunchboxes were made of pure polypropylene (PP), polypropylene-starch (PP-S), pure wheat-straw and sugarcane-straw (WS & SS) and Paper. The discrepancy of volatile aromatic substances was then analyzed using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) to study the possible mechanism beneath the variations of the influences of different lunchboxes on the aromatic properties of rice. Results showed that, compared with the textural attributes, the aroma was significantly and positively correlated with panelist's acceptability, among which, the aroma of starchy, sulfur and smoky are the most important ones. The moisture absorption plays an important role in affecting the aromatic characteristics of the packaged rice. While all lunchboxes have inhibitory effects on the production of volatile flavor substances including 2,6-Dimethylpyrazine, 2-Acetylpyrazine and γ-Octalactone, pure PP and PP-S lunchboxes generated undesirable flavor substances including 2-Ethyl-1-hexanl and Camphene, and thus reduced panelist's preferences. It was also found that the panelist liked the rice packaged by Paper lunchbox the best because of its better performance in maintaining the aroma of starchy and sulfur, the two substances that are associated with the higher concentration of ethereal and fruity volatile flavor substances. This study provides important information for manufacturers to understand how different disposable lunchboxes may impact the textural and aromatic properties of packaged foods.

The origin of Wxla provides new insights into the improvement of grain quality in rice

Appearance and taste are important factors in rice (Oryza sativa) grain quality. Here, we investigated the taste scores and related eating-quality traits of 533 diverse cultivars to assess the relationships between-and genetic basis of-rice taste and eating-quality. A genome-wide association study highlighted the Wx gene as the major factor underlying variation in taste and eating quality. Notably, a novel waxy (Wx) allele, Wx^la , which combined two mutations from Wx^b and Wxⁱⁿ , exhibited a unique phenotype. Reduced GBSSI activity conferred Wx^la rice with both a transparent appearance and good eating quality. Haplotype analysis revealed that Wx^la was derived from intragenic recombination. In fact, the recombination rate at the Wx locus was estimated to be 3.34 kb/cM, which was about 75-fold higher than the genome-wide mean, indicating that intragenic recombination is a major force driving diversity at the Wx locus. Based on our results, we propose a new network for Wx evolution, noting that new Wx alleles could easily be generated by crossing genotypes with different Wx alleles. This study thus provides insights into the evolution of the Wx locus and facilitates molecular breeding for quality in rice.

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.

Color-Induced Aroma Illusion: Color Cues Can Modulate Consumer Perception, Acceptance, and Emotional Responses toward Cooked Rice

Since rice is often cooked in many countries with different types of ingredients or seasonings, the surface colors of traditional rice meal items vary across cultural backgrounds. This study aimed to determine whether consumer perception, acceptance, willingness to eat, and emotional responses toward cooked rice samples could differ with their surface color cues. Milled rice was cooked with one of three food colorants: yellow, orange, and green, with milled (white) and un-milled (brown) rice cooked without colorants used as respective test and filler samples. Using a check-all-that-apply method, 98 rice consumers checked all aroma attributes they perceived by sniffing each of the four cooked-rice samples (white, yellow, orange, and green). They also rated the four samples with respect to attribute intensity, liking, emotional responses, and willingness to eat. The results showed that participants associated colored rice with specific ingredient-related aroma attributes (e.g., green color elicited sweet peas or spinach aromas). Color cues also affected ratings of attribute intensity, liking, willingness to eat, and emotional responses to cooked rice samples. In conclusion, this study provides empirical evidence that in the context of cooked rice consumption, color cues can elicit associated aromas and modulate consumer perception, acceptance, and evoked emotions to cooked rice.

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.

Improving Rice Grain Quality: State-of-the-Art and Future Prospects

Rice grain quality encompasses complex interrelated traits that cover biochemical composition, cooking, eating, nutritional, and sensory properties. Because rice endosperm is composed mainly of starch, rice grain quality is traditionally defined by characterizing starch structure and composition, which is then subsequently correlated with functional properties of the grain. The current proxy tests routinely used to describe rice grain quality preferences are rather limited to the estimation of apparent amylose content, gelatinization temperature, and gel consistency. Additional tests that characterize starch property, viscoelasticity, grain texture, and aroma are also employed in more advanced laboratories. However, these tests are not routinely applied in breeding programs to distinguish cooking quality classes to reflect evolving consumer preference and market demand. As consumer preferences in Asia and all over the world are diverse due to varied demographics and culture, defining uniform attributes to capture regional grain quality preferences becomes more challenging. Hence, novel and innovative proxy tests are needed to characterize rice grain quality to meet the demand for consumer preferences of commercially-released cultivars. In this chapter, the current methods employed in rice grain quality monitoring are succinctly reviewed. Future prospects for improvement are identified, introducing cutting edge technologies that can facilitate high-throughput screening of rice diversity panels and breeding lines. Aside from addressing the requirements for quality improvement in the traditional inbred rice breeding programs, we also tackled the need to enhance grain quality in the hybrid rice sector.

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.

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

The popcorn-like aroma compound 2-acetyl-1-pyrroline (2-AP) is a key contributor to the desirable aroma of fragrant rice and is also important in the aroma of other foods, such as pandan leaf, popcorn and Mediterranean sausage. It can be formed enzymatically in the rice grain as it grows and is also formed, as part of the Maillard reaction, when rice is heated. This review examines the formation of 2-AP in rice and other foods, particularly its formation during cooking, focusing on the importance of the Maillard reaction between reducing sugar breakdown products and 1-pyrroline derived from the amino acids proline and ornithine. The synthesis of 2-AP is discussed alongside the attempts that have been made to stabilise this relatively unstable compound. The analysis of 2-AP by instrumental techniques, particularly gas chromatography-mass spectrometry and gas chromatography-olfactometry, alongside the use of sensory studies, is also discussed.

Prospects of breeding high-quality rice using post-genomic tools

The holistic understanding derived from integrating grain quality and sensory research outcomes in breeding high-quality rice in the light of post-genomics resources has been synthesized. Acceptance of new rice genotypes by producers and consumers hinges not only on their potential for higher yield but recent emphasis has also been on premium-value genotypes that have the ability to satisfy consumer preferences for grain quality. This review article provides insights into how to link grain quality attributes and sensory perception to support breeding superior rice varieties. Recent advances in quality profiling and omics technologies have provided efficient approaches to identify the key genes and biochemical markers involved in rice quality traits. Emphasis has been given to the upcoming area of holistic understanding of grain quality and attributes derived from sensory evaluation to leverage integrative gene discovery strategies that enable breeding programs to efficiently tap the huge genetic diversity in rice for novel genes that enhance rice food quality.

Aroma chemistry of African Oryza glaberrima and Oryza sativa rice and their interspecific hybrids

BACKGROUND

To increase rice production in Africa, considerable research has focused on creating interspecific hybrids between African (Oryza glaberrima Steud.) and Asian (O. sativa L.) rice in an attempt to obtain the positive attributes of each in new cultivars. Since flavor is a key criterion in consumer acceptance of rice, as an initial inquiry we characterized and compared the aroma chemistry of selected cultivars of African O. sativa ssp. japonica, O. sativa ssp. indica, O. glaberrima, and their interspecific hybrids grown in West Africa, using gas chromatography-mass spectrometry, gas chromatography-olfactometry and descriptive sensory analysis.

RESULTS

Of 41 volatiles identified across seven representative rice cultivars grown in West Africa, 3,5,5-trimethyl-2-cyclopenten-1-one, styrene, eucalyptol, linalool, myrtenal and L-α-terpineol had not been previously reported in rice. Thirty-three odor-active compounds were characterized. 4-Ethylphenol and (E,E)-2,4-heptadienal were unique to O. glaberrima, and pyridine, eucalyptol and myrtenal were described only in an interspecific hybrid. Descriptive sensory analysis indicated 'cooked grain', 'barny' and 'earthy' attributes were statistically different among the cultivars.

CONCLUSION

The aroma chemistry data suggest that it should be possible to separate African cultivars into distinct flavor types thereby facilitating selection of new cultivars with superior flavor in African rice breeding programs.

Diversity of global rice markets and the science required for consumer-targeted rice breeding

With the ever-increasing global demand for high quality rice in both local production regions and with Western consumers, we have a strong desire to understand better the importance of the different traits that make up the quality of the rice grain and obtain a full picture of rice quality demographics. Rice is by no means a 'one size fits all' crop. Regional preferences are not only striking, they drive the market and hence are of major economic importance in any rice breeding / improvement strategy. In this analysis, we have engaged local experts across the world to perform a full assessment of all the major rice quality trait characteristics and importantly, to determine how these are combined in the most preferred varieties for each of their regions. Physical as well as biochemical characteristics have been monitored and this has resulted in the identification of no less than 18 quality trait combinations. This complexity immediately reveals the extent of the specificity of consumer preference. Nevertheless, further assessment of these combinations at the variety level reveals that several groups still comprise varieties which consumers can readily identify as being different. This emphasises the shortcomings in the current tools we have available to assess rice quality and raises the issue of how we might correct for this in the future. Only with additional tools and research will we be able to define directed strategies for rice breeding which are able to combine important agronomic features with the demands of local consumers for specific quality attributes and hence, design new, improved crop varieties which will be awarded success in the global market.

Descriptive analysis of flavor characteristics for black walnut cultivars

Seven black walnut cultivars, Brown Nugget, Davidson, Emma K, Football, Sparks 127, Sparrow, and Tomboy, were evaluated by descriptive sensory analysis. Seven trained panelists developed a lexicon for the black walnuts and scored the intensities of the samples for 22 flavor attributes. Results showed that the 7 samples differed significantly (P ≤ 0.05) on 13 of the attributes. For the majority of the attributes, only Emma K differed from the rest of the cultivars by being characterized with lower scores for black walnut ID, overall nutty, nutty-grain-like, nutty-buttery, floral/fruity, oily, and overall sweet. That sample also was higher in acrid, burnt, fruity-dark, musty/earthy, rancid, and bitter attributes. The remaining 6 cultivars showed few differences in individual attribute ratings, but did show some differences when mapped using multivariate techniques. Future studies should include descriptive analysis of other black walnut varieties, both wild and commercial, that could be grown and harvested for production.