## 3 Results
### Physico-Chemical Parameters of the Tested Rice Drinks
#### 3.2.3 Colour Parameters of the Studied Rice Drinks
In the case of rice drinks made from different types of rice, drinks made from white (from 2.92 \(\pm\) 0.18 to 4.12 \(\pm\) 0.06) and black (from 0.94 \(\pm\) 0.05 to 0.95 \(\pm\) 0.10) rice were characterised by much lower values for this parameter compared to results obtained in this work. Similar b* parameter values characterized rice drinks based on red rice to those obtained in this study (from 11.67 \(\pm\) 0.18 to 14.24 \(\pm\) 0.25) [31]. The authors explained the change in colour of various rice drinks with the degradation of compounds present in the raw material under the influence of the technological processes used [31]. Moreover, other authors have shown that in the case of red rice, both during storage and during various types of technological processing, significant colour changes occur, resulting from the oxidative degradation of proanthocyanidins present in the grain [40]. Some authors investigated colour in other beverages; for example, [PERSON] et al. (2019) [41], analysing the effect of homogenisation and heat treatment on the appearance of a lentil beverage, showed that the beverage had a naturally pinkish colour, which was attributed to the anthocyanins found in lentils. However, under the heat treatment used by the authors, the intensity of the pink colour was reduced, which was associated with the chemical degradation of the anthocyanins at high temperatures. Milk substitutes are relatively low-viscosity beverages, and the textural properties of these products are determined primarily by the particles present (e.g., fat droplets or plant tissue fragments), as well as the additives used, including thickening or stabilising substances [15], so it can be concluded that the resulting colour profiles of the rice drinks studied in this work, and determined by the L*a*b* colour space, were the result of the elemental composition of these products. Based on the measurements obtained for the colour parameters L*, a* and b*, the whiteness index (WI) was calculated (Table 4). The results show a high whiteness saturation of the tested beverages. This index averaged 81.79 \(\pm\) 2.55. Significant (\(p\) < 0.05) differences in this parameter were found between the individual rice drinks. The beverage with the significantly lowest whiteness index was RB_4 (77.82 \(\pm\) 0.06). Higher values were recorded for beverages RB_5, RB_10, and RB_3, as well as in beverages RB_7, RB_6, and RB_1. The beverages with the highest whiteness index values were RB_8 and RB_2, which did not differ in the value of this parameter. In contrast, the highest (\(p\) < 0.05) whiteness index among all the tested rice beverages was found in the beverage RB_9, reaching WI values of 86.20 \(\pm\) 0.18. Based on the analysis of the results obtained, it can be concluded that the whiteness index values obtained were most influenced by the parameter L* among the measured colour parameters. In the available literature, few studies on the whiteness index in rice drinks were found. Still, the authors investigated the influence of raw material and processing stage on the whiteness index in organic vegetable drinks. [PERSON] et al., (2017) [42] showed similar but slightly lower whiteness indices for beverages made from rice (66.49), quinoa (71.35), and brown rice (63.47) than those obtained in the present study, which, as for the individual parameters characterising the colour profile in the L*a*b* colour space, was influenced by the raw materials used in the production of the beverages, their percentage share in the beverage base composition, the processing method, or the additives used, such as colouring agents, emulsifiers, stabilisers, or thickeners [43]. In a study performed by the same authors, the whiteness indices for different plant-based beverages ranged from 51.73 (for macadamia beverage) through 56.31 (for hazelnut beverage), 60.21 (for oat beverage), 65.57 (for cashew nut drink), 67.36 (for almond drink), 67.75 (for coconut drink), 68.49 (for hemp drink), to 71.35 (for quinoa drink) or 72.17 (for soy drink) [42].