The results of the proximal composition exhibited some variations with respect to the values reported in the literature; it is observed that both substrates had a high fiber content (Table 1). These are expected results, because the composition of the plants depends on the growing conditions, as well as on the variety and geographic location, among other factors involved in their development and processing . The composition of these substrates shows potential for their use in the production of cellulases, due to the considerable content of cellulose, which is the main inducer of these enzymes .
The capacity of a support to absorb water is known as WAI, and CHP is the portion of water that cannot be used by the microorganism for the development of its metabolic reactions, because it is strongly bound to the substrate. Values similar to those obtained in the present study (Table 2) have been reported in materials used in solid-state fermentation processes as immobilization vehicles , for the production of polyphenolic compounds , ellagic acid , and β-fructofuranosidase . The highest WAI was presented by green tea, which can be associated with low-fat content and a high amount of fiber .
Solid-state fermentation processes are triphasic systems with low humidity, substrates with low thermal conductivity, and a continuous gas phase. These produce a shortage in heat transfer and with it, an increase in localized temperature, decreasing humidity. Therefore, substrates with high WAI and low CHP are preferable for its development, allowing the incorporation of water without compromising the aeration of the system and its productivity [36, 37]. Therefore, these substrates are suitable to be used with SSF.
Radial growth rate
Figure 1 shows the growth kinetics of the different strains on the evaluated substrates. Table 3 details the growth rates of the different strains. It is observed that T. asperellum AFP with CT as support presented the highest radial growth rate 0.409 ± 0.021 mm/h, followed by A. niger 28 A and 20A on T with 0.224 ± 0.004 and 0.224 ± 0.030 mm/h, respectively.
The A. strains showed very similar speeds to each other, depending on the substrate. Considering that both substrates have very similar values in soluble reducing sugars, the difference exhibited in radial growth rates is not associated with this factor. The growth rate of the Aspergillus strains is higher in T, followed by TC and finally in C.
This behaviour follows the expected trend, given by the WAI and CHP values. Because T has the highest WAI concerning its CHP, which favours the development of metabolic functions and with it the microbial growth . Likewise, T and TC have the pH closest to 5, considered to be the optimum for the development of Aspergillus . Also, C has some components with antifungal properties, such as ferulic acid  and caffeine [13, 39], that can hinder the development of the proven Aspergillus strains.
Trichoderma presented the highest growth using TC as a support, and its speed decreased when using C following the same pattern of the Aspergillus strains provided by the factors of WAI, PHC, and pH. However, he was inhibited using T as a support. This may be an indication that the valued Trichoderma strain shows sensitivity to some antifungal components of tea, such as EGCg (epigallocatechin-3-gallate) and phenyl lactic acid , which had a decreased concentration in TC.
Endocellulase activity plate assay
The degradation halos produced by the plate technique were analysed through a Tukey mean test (p > 0.05). The widest degradation halos were produced by the extracts obtained from treatments 28A TC, 28A T, 20A T. They did not show a significant difference concerning the control (Figs. 2, 3).
The highest degradation halos were generated by the extracts produced by the A. niger strains. This phenomenon is associated with what has been reported by Ximenes et al. , who indicate that Aspergillus cellulases are more resistant than Trichoderma cellulases to the inhibitory effect of polyphenols, which are found in abundance in both substrates [42, 43].
In the case of the Aspergillus strains, the highest activities were produced using T and TC as support. Both substrates have a pH quite close to 5.5, in which it is reported that the optimum point of production of a tannin-degrading protein complex is presented, inhibiting the antimicrobial effect produced by the tannins present in the worked substrates. Furthermore, they are within the range of pH 4.5–5 in which higher cellulase titers are usually produced , further highlighting that both T and TC have the highest WAI and CHP, which allows a better development of metabolic functions , and a lower caffeine content that also affects enzyme production .
The 28A T and 20A T treatments presented the highest cellulase activities by plate method and the highest growth rates, being significantly the same in both parameters. For this reason, the 28A T treatment was selected to continue the work.
Evaluation of the use of mineral enrichment media in the production of cellulase enzymes using green tea residues as support
The enzymatic activities obtained with each treatment were analysed through a Tukey mean test (p > 0.05). Production of 2.4 ± 0.3, 2.2 ± 0.42, and 2.5 ± 0.45 FPU/g was obtained using water, Mandel's medium, and Czapek-Dox, respectively. Enzymatic titers comparable to those obtained by other authors were obtained (Table 4). It was found that there is no significant difference in the production of FPU activity when using water or the Mandels and Czapek–Dox mineral enrichment media (Fig. 4).
The induction of cellulase induction is strongly influenced by carbon, nitrogen, and physical parameters such as pH, temperature, and incubation time . The lack of an effect that drives the production of cellulase activity by the mineral media can be associated with a saturation of nutrients in the medium. High concentrations, some minerals like Mn, Co, Zn, and Fe, can cause a decrease in cellulase activity yields . These results indicate that substrate T has sufficient nutrients intrinsically and does not require additional supplementation for the production of total cellulase activity by A. niger 28A.