- Journal Details
- Format
- Journal
- eISSN
- 2544-4646
- First Published
- 04 Mar 1952
- Publication timeframe
- 4 times per year
- Languages
- English
Lignocellulose (LC) present in the plant cell wall provides strength and protection against pathogens. Lignin, cellulose, and hemicelluloses are the main constituents of the LC (Yang et al. 2004). Cellulose is a homopolysaccharide while hemicelluloses are derived from different sugars, the composition of which depends on the type of plants and weather conditions. Xylose is the main constituent of most of the hemicellulose and it is usually arranged in shorter chains of ~ 200 units (Brown et al. 2009) to comprise xylan.
Considering heterogeneity in the structure of hemicelluloses, microbial degradation of hemicellulose requires various enzymes; xylanases play a major role in this context. Pectinases, on the other hand, attack on a pectic portion of the LC masses. Since abundantly found LC substrates are rich in fermentable components, therefore, these are perceived as the promising raw materials for biorefineries. Hence, the bioconversion of LC is an important subject in biological research (Otero and Nielsen 2010). Previously, enzymatic digestion of several LC materials has been reported such as corncob (Kahar et al. 2010), Kraft paper-mill sludges (Kang et al. 2010), and sugarcane bagasse (Buaban et al. 2010). It suggests that LC materials can be saccharified using an enzyme(s) and can provide a cheaper source of raw materials for many industries. However, the selection of an LC substrate for industrial exploitation mainly depends on local agricultural practices, as availability of the substrates remains a decisive factor. Banana peels (BP) is a waste LC substrate that is generated by the fruit that remains available throughout the year in Pakistan and, hence, can be investigated for its possible application as a promising LC substrate.
Banana is one of the most popular fruit in the world owing to its nutritional value, hygiene, cost-effectiveness, and its digestibility. In South Asia, it is the leading fruit, grown over a hundred thousand hectares of cultivated land. Consequently, thousands of tons of BP are accumulated as the domestic and food industry’s waste, which is not effectively utilized. With considerable quantities of lignin (6–12%), pectin (10–21%), cellulose (7–10%), and hemicelluloses (6–9.4%) (Emaga et al. 2008), BP has been reported as an effective fermentation substrate (Kiranmayi et al. 2011; Rehman et al. 2014). Various studies have been conducted to produce industrially important enzymes using BP including alpha-amylase by
The enzyme preparation was harvested by shaking the fermented BP in 40 ml of 0.05 M sodium citrate buffer (pH – 4.8) and Tween 80 (0.5%) on an orbital shaker for 1 h at 150 rpm at 30°C and, then, filtering the slurry through several layers of muslin cloth and a Whatman number 1 filter paper. The extract was centrifuged at 6000 × g for 20 min, and the supernatant was used as a crude enzyme preparation that was stored at –20°C until used for the determination of the enzyme activity.
The submerged fermentation was further investigated by adopting one variable at a time strategy (Shariq et al. 2018). To optimize the temperature for the production of xylanase and pectinase the flasks were incubated at a temperature from 25 to 40°C. Likewise, optimum pH was determined by cultivating the strain MS 16 at an optimum temperature in the medium with pH adjusted to 4–6.5. In a similar manner, the substrate concentration (0–1.6%), the effect of supplementation (0.5% xylan or pectin), and the incubation period (5–7 days) were studied.
Fungal strains have frequently been reported for the production of industrially important enzymes from waste materials. The hyphal mode of growth enables them to penetrate through the substrate and to utilize fermentable components by elaborating hydrolases. The availability of banana makes its waste, BP, a promising substrate for the fungal fermentation to obtain value-added products. Previously,
Fig. 1.
Effect of medium along with banana peels (BP) on the pec tinase and xylanase production by
When the effect of temperature on pectinase production was studied, it was observed that there wasn’t much variation in the titers of pectinase when the cultivation temperature varied from 25 to 35°C (Fig. 2). However, a drastic decrease in the levels of pectinase was observed when the temperature was adjusted to 40°C. Temperature affected the production of xylanase differently as it was observed that Smf could be carried out at a temperature from 20–40°C without affecting the enzyme yield, though titers of the enzymes were slightly higher at 30 and 35°C. This finding was in agreement with the results obtained by Naseeb et al. (2015).
Fig. 2.
Effect of temperature on pectinase and xylanase production under submerged (SmF) and Solid state fermentation (SSF) of banana peels by
To investigate the induction of pectinase and xylanase by the corresponding substrate (pectin or xylan), the two substrates were added separately or in combination, in BP containing MSM and the production of both the enzymes was studied. It was noted that pectinase production was enhanced when only pectin or pectin with xylan was added to the MSM + BP (Fig. 3); however, the production was negatively affected if only xylan was added to the MSM + BP. Likewise, xylanase production by MS16 was induced in the presence of xylan supplemented MSM + BP or xylan and pectin containing MSM + BP. Previously, supplementation of pectin and xylan to apple peel powder was found to induce pectinase and xylanase, respectively, under SSF by
Fig. 3.
Effect of supplementation of pectin and xylan to banana peels containing medium on the production of pectinase and xylanase from
The pH value of the medium influences the production of an enzyme by regulating the solubility of the nutrients, the permeability of the cell membrane, and ionization of amino acids and/or proteins. Usually, fungal strains grow better under acidic conditions;
Fig. 4.
Effect of pH on pectinase and xylanase production from
In the submerged fermentation the varying concentrations (0.25–1.6%) of BP were tested to determine the optimal concentration for the production of the enzymes. MS16 produced the highest titers of pectinase in MSM with 1% BP and xylanase in 0.25% BP containing medium (Fig. 5).
Fig. 5.
Effect of banana peels concentration on pectinase and xylanase production from
After studying optimum levels of the above-mentioned factors, the enzyme production was studied by taking aliquots intermittently and the optimum incubation period for both the enzymes was determined. The data showed that pectinase production was maximum on day six, thereafter, it decreased slightly, while xylanase production dropped significantly when the incubation period extended from five days (data not shown).
In SSF, the xylanase production increased with the supplementation of 0.5% xylan alone or with pectin, while it decreased when the pectin was supplemented without xylan (Fig. 3). The supplementation of pectin and/or xylan did not exert the significant effect on the pectinase production by MS16. In their studies, Rehman et al. (2014) reported about the indifferent pattern of pectinase production upon supplementation of pectin to BP under SSF by a fungal co-culture.
The moisture content is one of the important factors for solid-state fermentation but it did not affect the activity of xylanase; it was almost the same but the pectinase activity was maximal at 65% moisture content (Fig. 6) that corroborated with the findings of Padma et al. (2012) where 65% moisture was optimal to obtain the highest levels of polygalactouronase by SSF of BP.
Fig. 6.
Effect of moisture content on pectinase and xylanase production under solid-state fermentation of banana peels.
Finally, the production of the enzyme was studied under optimum conditions for a period of 5–7 days and enzyme activity was assayed. The maximum pectinase was produced in five days of incubation while xylanase production was the highest after seven days of incubation (data not shown).
Fig. 7.
Effect of temperature on pectinase and xylanase activities produced under solid-state (SSF) and submerged fermentation (Smf).
The studies on the effect of pH on the enzyme activity showed that pectinase and xylanase were catalytically most active at pH 5.0 and 5.5 (Fig. 8), respectively, and this property remained unaffected when the production method was changed from Smf to SSF. Generally, fungal enzymes work well under acidic conditions. For instance, Kiranmayi et al. (2011) reported that a value of 6.0 as the most suitable pH for cellulase activity from
Fig. 8.
Effect of pH on pectinase and xylanase activity produced from
Banana peels appeared as a suitable substrate for the simultaneous production of pectinase and xylanase from
Fig. 1.
Fig. 2.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. 6.
Fig. 7.
Fig. 8.
