To evaluate the potential of the industrial waste of Rojo Brillante persimmon as a source for value-added products. The antioxidant compounds present in persimmon industrial waste (peel and calyx) and the suitability of this bagasse to be used as a substrate secondgeneration bioethanol production are studied and discussed. Both value-added products would contribute to the valorization of persimmon fruit residues, which are expected to increase to a higher extent in subsequent years, thus contributing to the food industry sustainability and circular economy. MethodsAntioxidant properties were evaluated by analyzing total phenol content, soluble tannins, flavonoids and antioxidant capacity of the waste, consisting of the peel and calyx of the fresh-cut persimmon industry. In a different approach, several fermentation and saccharification processes were assayed in order to valorize the waste as a substrate for bioethanol production: direct fermentation (DF) of the waste (with water addition, sterilized or not) was carried out and compared with simultaneous saccharification and fermentation (SSF) of the waste (with and without water addition). ResultsThe amount of phenols (59.2 ± 0.4 mg AGE/100 g FW), flavonoids (7.5 ± 0.4 mg QE/100 g FW) and tannins (11.43 ± 0.08 g AGE/100 g FW), as well as the antioxidant capacity (16.67 mg TE/100 g FW) of persimmon industrial waste were in the range of the pulp values. Persimmon waste was especially rich in carotenoids: β-carotene (400 ± 7 µg/100 g FW) and lycopene (194.3 ± 0.7 µg/100 g FW), these being values higher than in the whole fruit or pulp. Bioethanol production was more successful when a simultaneous saccharification and fermentation process was directly applied on the grinded waste (0.36 ± 0.010 gethanol/gsugar), as compared to the other DF and SSF assayed. ConclusionsPersimmon waste can be considered a good candidate for obtaining value-added products.Carotenoids could be extracted from this waste, but it is recommended to develop food ingredients in the form of flours of powders to be used as functional ingredients.Persimmon waste is also recommended as a substrate for second-generation bioethanol production, either alone or mixed with other food residual biomass.
Electrochemical impedance spectroscopy (EIS) has been used for monitoring the enzymatic pineapple waste hydrolysis process. The system employed consists of a device called Advanced Voltammetry, Impedance Spectroscopy & Potentiometry Analyzer (AVISPA) equipped with a specific software application and a stainless steel double needle electrode. EIS measurements were conducted at different saccharification time intervals: 0, 0.75, 1.5, 6, 12 and 24 h. Partial least squares (PLS) were used to model the relationship between the EIS measurements and the sugar determination by HPAEC-PAD. On the other hand, artificial neural networks: (multilayer feed forward architecture with quick propagation training algorithm and logistic-type transfer functions) gave the best results as predictive models for glucose, fructose, sucrose and total sugars. Coefficients of determination (R2) and root mean square errors of prediction (RMSEP) were determined as R2 > 0.944 and RMSEP < 1.782 for PLS and R2 > 0.973 and RMSEP < 0.486 for artificial neural networks (ANNs), respectively. Therefore, a combination of both an EIS-based technique and ANN models is suggested as a promising alternative to the traditional laboratory techniques for monitoring the pineapple waste saccharification step.
Electrochemical Impedance Spectroscopy (EIS) has been used to develop a methodology able to identify and quantify fermentable sugars present in the enzymatic hydrolysis phase of second-generation bioethanol production from pineapple waste. Thus, a low-cost non-destructive system consisting of a stainless double needle electrode associated to an electronic equipment that allows the implementation of EIS was developed. In order to validate the system, different concentrations of glucose, fructose and sucrose were added to the pineapple waste and analyzed both individually and in combination. Next, statistical data treatment enabled the design of specific Artificial Neural Networks-based mathematical models for each one of the studied sugars and their respective combinations. The obtained prediction models are robust and reliable and they are considered statistically valid (CCR% > 93.443%). These results allow us to introduce this EIS-based technique as an easy, fast, non-destructive, and in-situ alternative to the traditional laboratory methods for enzymatic hydrolysis monitoring.
The hydrolytic action of Aspergillus niger and Trichoderma reesei commercial cellulases, alone or combined with A. niger hemicellulase, against industrial pineapple waste as a previous step to produce bioethanol was investigated. Methods Enzymatic hydrolysis experiments were conducted in static conditions in an incubation oven, by adding the corresponding enzyme mixture to the pineapple waste (combinations of 0, 0.1, 0.2 and 0.4 (w/w) of cellulase from A. niger or T. reesei and hemicellulase from A. niger). pH and total soluble solids were examined along the treatments, and the sugar profile in the final hydrolysates was evaluated by High-Performance Anion-Exchange Chromatography. Results T. reesei cellulase exhibited a significantly faster initial hydrolysing rate than A. niger cellulase (0.258±0.004 vs. 0.15±0.07, for the maximum enzyme concentrations assayed), although differences regarding soluble sugars increments were not significant at the end of the treatment (0.349±0.009 vs. 0.34±0.05). Glucose, fructose, sucrose, arabinose, xylose and cellobiose were identified in the hydrolysates. Increasing enzyme concentration (cellulase or hemicellulase) produced an increase in total and fermentable sugars released (17 and 11%, respectively, for the maximum enzymatic concentration assayed); besides, a synergistic effect of combining hemicellulase and cellulase was identified. Accumulation of cellobiose (up to 4.4 g/L), which may slow down hydrolysis, evidenced the weaker β-glucosidase activity of T. reesei cellulase. Due to its performance and the lower cost of the enzyme, A. niger cellulase was chosen as an alternative. Conclusions 2 Commercial A. niger cellulase represents an efficient alternative to T. reesei cellulase for the saccharification of industrial pineapple waste, especially when combined with a hemicellulase. Total sugars present in the final hydrolysates indicated that A. niger cellulase performed similarly at a lower cost, with no cellobiose accumulation. However, if processing time is a limiting factor, Trichoderma reesei cellulase could be the one preferred.
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