Chemistry Medicine
AgriculturalAndFoodSciences,1970-2015-Agricultural And Food Sciences-2012.jsonl.gz.gz
Agricultural And Food Sciences
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Thermostability of xylanolytic enzymes produced by Lentinula edodes UFV70

Xylanolytic enzymes produced by Lentinula edodes UFV70, cultivated in eucalyptus sawdust/rice bran medium, were stable at 50, 60 and 65°C for 21 hours, losing only 15–25% activity. Fungus incubation at 50°C for 12 hours and at 65°C for 24 hours increased the amount of xylose produced.

The increased expansion of agro-industrial activity has led to heavy accumulations of lignocellulosic residues that often contaminate the soil. Lignocellulose is the most abundant renewable biomass available on the planet, which consists of three major groups: cellulose, hemicellulose, and lignin (14).
Hemicellulose classification is based on the main sugar unit, where a hydrolyzed polymer that yields xylose is considered a xylan (12).
Lentinula edodes is a white rot fungus that grows on lignocellulosic residues, such as Eucalyptus sawdust and rice bran (3) . Its enzymes can be used in biotechnological applications, i.e., to create xylose for xylitol production (15), lignolytic enzyme production (2,4), and applications in other biotechnological processes, such as bioethanol production (6), and to increase the final brightness ceiling in bleached pulp (13).
The thermostability of xylanolytic enzymes is an important characteristic that allows for their application in industrial processes (13). These enzymes must be stable at high temperatures for use in pulp bleaching, for example (13). It is known that thermophilic fungi produce thermostablexylanase, which retains its catalytic activity for many hours at high temperatures ranging from 80-100 ˚C (5,9,16).
This study aimed to evaluate agro-industrial residue incubation conditions to maximize the amount of xylose produced, which is released by the enzymes from Lentinula edodes grown in Eucalyptus sawdust/rice bran medium. It was hypothesized that if lignocellulosic material, colonized by the fungus, was incubated at a temperature at which the fungus was unable to grow, but its xylanolytic enzymes were still able to hydrolyze the polysaccharides in the growth medium, then xylose concentrations would increase in the hydrolysates. The apparent specific activity of xylanolytic enzymes was detected after the second week, varying from 0.5 to 1.5 U mg -1 of protein (data not shown). The temperature for maximum apparent specific xylanolytic activity, 70 ºC (data not shown), was similar to thermophilic fungi, such as Thermomyces lanuginosus (16), but higher than that previously found in other L. edodes strains (50-60 ºC) (7,8,11). Xylanolytic enzymes were stable in a temperature range of 35-65 ºC for 3 hours. At 70 ºC, the activity was 11% lower than that of the control (data not shown). When the activity was measured after pre-incubation, it was 25, 20, and 15% lower after 21 hours of pre-incubation at 65, 60, and 50 ºC, respectively ( Figure 1). The maximum apparent activity occurred at a higher temperature (70 ºC) than previously reported (50-60 ºC) (7,8,11). Furthermore, these enzymes were considerably stable when pre-incubated up to 65 ºC, for up to 21 hours (Figure 1).
Compared to the reported 50% loss of -xylanase activity at 60 ºC after 6 hours for this same species (7), this current study found these enzymes to be much more stable. These differences may be due to the use of crude enzymatic extracts in this study, instead of purified enzymes (7). Some substances present in the crude extracts may have had an influence on the thermostability of these enzymes. Also, the current study used a different strain, L. edodes UFV70. These results are promising, because the use of crude extracts is a less expensive process than using enzymes.  -Control (xylose concentration in samples that were collected before thermal treatment); • -12 hours at 65 ºC; ♦ -24 hours at 65 ºC; -12 hours at 50 ºC; -24 hours at 50 ºC.