*6.2.1 Effect of planting density on 2-acetyl-1-pyrroline content*

2AP content decreases with an increase in planting density. The content of 2-AP in rice grains obtained during the early season will be stored for 6 months. However, other seed quality attributes at the exception of head rice yield and grain vitreosity were not affected by planting density [115].

## *6.2.2 Effect of harvesting time on 2-acetyl-1-pyrroline content*

Reduction in 2AP was observed with increasing harvest date during the early season. During the late season, however, the concentration of 2AP is gradually decreased from 10 DAH and seemed to stabilize at 40 DAH, a reduction rate of 60%. However, it is well compensated for by the high level of 2AP in both brown and white rices, which remains significant even after a storage period of 3 months at ambient temperature [116].

#### **6.3 Processing factors**

#### *6.3.1 Cooking*

Presoaking is a traditional pretreatment before cooking. It would result in uniform cooking and less cooking time. Presoaking for 30 min before cooking resulted in significant increase in sewer/animal flavor and summed negative flavor attributes, and significant decrease in sweet taste and summed positive flavor attributes, mainly as a result of an increase in sulfur-containing free amino acids and their breakdown products [19].

According to [117], divided the cooking process into four stages and identified the major compounds of Japanese rice cultivar Akitakomachi. In stage I (25 min, from the start of heating to start of steam coming out of rice cooker) were aldehydes such as n-nonanal, n-decanal, and (E)-4-nonenal. The dominating compounds identified at cooking stage II (13 min, from the start of steam coming out of rice cooker to the end of steam coming out of rice cooker) were hexadecanoic acid and tetradecanoic acid. The major compounds identified at cooking stage III (10 min, from the end of steam coming out of rice cooker to automatic stop of heating) and IV (keeping the rice warm for another 30 min) were aldehydes and fatty acids.

#### *6.3.2 High hydrostatic pressure and superheated processing (HHP)*

High hydrostatic pressure (HHP) had stabilized effects on low molecular weight volatiles [118], and it is one of the effective processing to improve products flavor. HHP was thought to be a good pretreatment option to enhance aroma quality of cooked rice. HHP process enhanced the formation of aldehydes, alcohols and

ketones in germinated brown rice [119]. The volatile compounds in rice were cooked by superheated steam rice cooking machine were compared -with those of ordinary cooked rice [105].

#### *6.3.3 Roasting and parboiling*

While roasting there is a change in volatiles by the Maillard and caramelization reactions, and consequently form unique flavor, and usually increase the popularity of consumers. Increases the content of heterocycle compounds and decreases the content of hydrocarbons and benzene derivatives by roasting process [120]. Parboiling cause concomitant changes in the physical, chemical, and nutritional properties of grains, and consequently greatly affect organoleptic and other qualities. Hydrothermal treatment during parboiling would inactivate lipases, and inhibit the development of off flavors [121]. Hence, it was a good method to keep rice aroma during storage.

### *6.3.4 Milling*

Un-milled black rice contained significantly larger amounts of total volatiles than milled black rice [122]. That is, the volatile compounds were mainly distributed in the bran layer of black rice (624 ± 17.7 ng g − 1), and significantly decreased by milling, especially the contents of acids, esters, and alcohols. When milling aromatic rice (Cheonjihyang-1-se), hexan-3-one, benzene, 2-pentylfuran, and pentanal decreased to 79%, 70%, 54%, 78% with milling time from 10s to 140 s, while (E)-non-2-enal, pentadecanal, (5E)-6,10-dimethylundeca5,9-dien- 2-one, and menthol increased 252%, 185%, 172% and 159% [123].

#### **6.4 Storage factors**

It was reported that, proteins, lipids and carbohydrates were decomposed into volatiles contributing rice odor during storage [124]. Enzyme catalyzed reactions were drastically inhibited at low temperature. This was one reason for slower deterioration of rice aroma. In general, lower storage temperature and better packaging materials would be more appropriate for aromatic rice to better maintain desirable rice aroma. OPP/Al/LLDPE package was superior to Nylon/LLDPE package, and storage at lower temperature (15°C) was better than ambient temperature, since they better retarded the formation of lipid oxidation products and other characteristic odorants in organic red aromatic rice [125]. Some paper assumed that lower temperature during storage would minimize volatilization of 2AP from rice [126, 127].

#### *6.4.1 Effect of storage time and temperature on 2-acetyl-1-pyrroline content*

Fragrant rice harvested in June and kept for 6 months at – 4°C contained up to four times 2-AP in all forms (brown and white), compared to those kept at 30°C. High losses of 2-AP occurred under a very warm condition of 30°C. There were also significant differences in the concentration of 2-AP between samples collected in November with losses of 25 to 35% occurring after storage of 3 months at 20°C compared to 8°C [115].

Therefore, insights into extraction and quantification methods and various factors affecting the quality of aroma are essential, and also modern biotechnological advances like Transcription Activator Like Effector Nuclease (TALENs), Zinc Finger Nuclease (ZFNs) and Clustered Regularly Interspaced Short Palindromic

*Rice Aroma: Biochemical, Genetics and Molecular Aspects and Its Extraction… DOI: http://dx.doi.org/10.5772/intechopen.98913*

Repeats (CRISPR) associated endonuclease Cas9 (CRISPR/Cas9) are being entrusted in improving the rice aroma content and quality. Researchers succeeded in editing *Badh2* gene and generating high yielding fragrance rice varieties by using TALENs [128] and CRISPR/CAS9 [129–131] technologies, which led to increased accumulation of 2AP.
