## 3 Results and Discussion  
### Effect of High CO\({}_{2}\) in CA on Physiological Attributes  
High water loss through transpiration is the major cause of quality reduction in leafy produce, including culinary herbs such as mints. High-surface-area-to-volume ratios and number of stomata in leaf tissues result in high rates of water loss, which as a consequence, affect marketable weight and visual quality, and may affect the physiology and ability to resist pathogen invasion [1]. During the first 5 day storage, CO\({}_{2}\) treatments significantly maintained weight loss to the levels close to the CTRL (Figure 1A). The highest weight loss was observed in 5% CO\({}_{2}\) at day 10, while that of the CTRL group was the lowest. The relationship betweenlevel of CO\({}_{2}\) and stomata closure has been studied [36]. However, no unequivocal conclusion could be drawn. CO\({}_{2}\) concentration of the air may or may not induce stomatal frequency and the results may vary from one genotype to another [37]. Throughout the respiration process, oxygen is consumed, thus producing by products, i.e., water, carbon dioxide, and energy. The latter is the vital resource for subcellular activity. Low O\({}_{2}\) atmospheric conditions may result in a reduction in the respiration rate due to the reduction in overall metabolic activity [8; 38]. The influence of CO\({}_{2}\) concentrations on respiration, however, depends upon the type and developmental stage of the commodity, and time of exposure [38; 39]. Based on our results, higher atmospheric percentages of CO\({}_{2}\) may accelerate the respiration and transpiration of freshly cut spearnints, which declined thereafter.  
The determination of firmness or texture is used to describe the freshness of freshly cut herbs [40]. In our present study, the force (N) used to compress spearmint leaves stored in CA significantly increased with the CO\({}_{2}\) concentration and storage times (Figure 1B and Table 1). This is not in agreement with other studies where the texture attribute was independent from the concentrations of gases [40; 41]. Magu  
Figure 1: Effect of CO\({}_{2}\) concentrations in the control atmosphere (CA) storage of cut spearmint on weight loss (\(\%\), (**A**)), firmness (N, (**B**)) and CIE space L\({}^{*}\) (**C**), a\({}^{*}\) (**D**), b\({}^{*}\) (**E**) and the difference of the colour space or delta E (**F**). Vertical bars represent standard error (\(n=3\)).  
advised that a water loss of the stored commodities greater than 3% may cause the development of a rubbery texture. This is what possibly occurred in our case, as all CO2 treatments led to an increase in weight loss, thereby leading to the loss of freshness and as a result the texture became tough rather than crispy.  
CO2 treatments also altered leaf colour surface (Figure 1C-F). L* and b* significantly decreased, while the a* value increased; the results in the CO2 treatments were apparent from day 5 onwards. The higher percentage of CO2, the grater the alteration of these values; a reduction in the lightness (L*) and yellowness (b* value) were also observed in the elevated CO2 packaging of cilantro, possibly illustrating the discolouration (browning) of the leaves [40]. The increase in a* value also reveals the loss of greenness of the leaf, which is as a result of the ongoing loss of fresh weight due to water also leading to discoloration and the degradation of the chlorophyll pigment [1; 39; 42]. The physical quality of cut spearmint was also evaluated based on the difference in the colour surface values to the fresh sample. It appears that lower levels of CO2 treatments are able to maintain the overall colour changes in the refrigerated temperature within the consumer acceptable range (<3.5) for 5 days.