Except for PC1 (Fig. 4A), the visible region of spectrum presented high loadings in all PC, with high weights in this region. PC1 is characterized by negative loadings around 1900 nm, typical of OH first stretch overtone probably due to cellulose [25]. This indicates that the coffee husks have lower percentages of cellulose than coconut and banana biomasses, which is supported by analytical data (Reference method) shown in Fig. 3, where it is possible to observe a higher average value of glucose (assigned to cellulose) for coconut and banana, than for coffee. On the other hand, PC2 was characterized by positive loadings at 540 nm, characteristic bands of chlorophyll [22] and, as expected, that differentiates leaf samples rich in these photosynthetic pigments, as well as the coffee samples with positive scores (Fig. 4B). PC3 and PC4 have positive loadings at 470 and 677 nm, both associated to chlorophyll [22]. Most coffee samples and some banana samples show negative scores in PC3, probably assigned to C―H or CH2 stretch of lignin structures, associated with the negative loadings of 760 nm in PC3.