Coffee is one of the main economic crops in the world and is now widely grown throughout Taiwan. The process of roasting coffee begins with the heating and smooth expansion of raw beans, which leads to changes in appearance and color while affecting the flavor and taste of coffee. So far, most coffee manufacturers have used visual inspection or colorimeter methods to identify differences in coffee quality. Moreover, there is no literature discussing the correlation of roasted bean color with caffeine and chlorogenic acid content. Therefore, the purpose of this experiment was to analyze the chlorogenic acid and caffeine content and their correlation with bean color under different roasting degrees and from different sources to establish basic data for the rapid identification of coffee quality in the future. In this experiment, the coffee Coffea arabica typica from Dongshan, Gukeng, and Sumatra’s Indonesian rainforest was used, and the beans were roasted into four degrees: raw bean, light, medium, and dark roast, to investigate the appearance of the coffee beans and its correlation with caffeine and chlorogenic acid content. The results showed that with a higher roasting degree, caffeine content increased gradually, except for Indonesian beans, but the chlorogenic acid content in all samples showed a declining trend with the increase in roasting degree. The correlation between the chlorogenic acid content and the color space value of the coffee bean color shows that L*, a*, and h° in both ground and unground coffee are highly correlated. The C* value of the ground and unground coffee showed a correlation coefficient of r = 0.159 ns and 0.299 ns, respectively. The correlation between the caffeine content and the color space value of the unground coffee bean shows that the a*, b*, and C* value is highly correlated with the caffeine content. The color space values of ground coffee beans show no correlation with caffeine.

Papaya fruit is one of economic crops in Taiwan, mostly eaten as table fruits. In some Asian countries, unripe papaya fruit is eaten as salad and this led to trends in Taiwan as well. However, unripe papaya fruit may taste bitter during cool seasons. Glucosinolate and cyanogenic glucoside are among the substances that cause bitter taste in many plants, which can also be found in papaya. However, there is still no report about the relationship between seasons and bitter taste in papaya fruits. Thus, the purpose of this study is to investigate the glucosinolate biosynthesis and its correlation between bitterness intensity during cool and warm seasons. The bitterness intensity was highest at the young fruit stage and decreased as it developed. In addition, the bitterness intensity in cool season fruits is higher than in warm season fruits. Cyanogenic glucoside and BITC content showed negative correlation with bitterness intensity (r = −0.54 ***; −0.46 ***). Phenylalanine showed positive correlation with bitterness intensity (r = 0.35 ***), but its content did not reach the bitterness threshold concentration, which suggested that phenylalanine only acts as cyanogenic glucoside and glucosinolate precusors. Glucosinolate content showed positive correlation with bitterness intensity at different developmental stages (r = 0.805 ***). However, the correlation value in different lines/cultivars decreased (0.44 ***), suggesting that glucosinolate was not the only substance that caused bitter taste in immature papaya fruits.

Papaya milk, a mixture of papaya pulp and dairy milk, is one of the most popular beverages in Taiwan. However, the enzymes present in papaya can cause accumulation of hydrophobic amino acids, resulting in a bitter taste of papaya milk. Thus, it is important to select papaya cultivars without the potential to form the bitter taste, but it is difficult to select these papaya cultivars using a sensory test. The purpose of this research was to investigate the relationship between the intensity of the bitterness with the contents of proteins and free amino acids. The results indicated that neither milk nor papaya alone tastes bitter. Heating the milk or the papaya before mixing and mixing only papaya latex with milk confirmed that an enzyme in papaya causes the bitter taste in papaya milk. The intensity of bitterness positively correlated with the contents of total soluble protein, free amino acids and the phenylalanine and tyrosine/tryptophan contents. Analyses using different papaya accessions in different seasons showed that tyrosine/tryptophan (r = 0.613***) and phenylalanine (r = 0.612***) correlate more strongly with bitterness intensity than the total soluble protein (r = 0.258*) or free amino acids (r = 0.38**). In this drink, milk provides the substrates to form the bitter substances, but the enzymes in the papaya are needed for the reaction to occur. The levels of the amino acids phenylalanine and tyrosine/tryptophan showed the highest correlation with the intensity of bitterness.