*Article* **A Comprehensive Bioprocessing Approach to Foster Cheese Whey Valorization: On-Site** β**-Galactosidase Secretion for Lactose Hydrolysis and Sequential Bacterial Cellulose Production**

**Iliada K. Lappa , Vasiliki Kachrimanidou , Aikaterini Papadaki , Anthi Stamatiou, Dimitrios Ladakis, Effimia Eriotou and Nikolaos Kopsahelis \***

> Department of Food Science and Technology, Ionian University, 28100 Argostoli, Kefalonia, Greece; lappalida@gmail.com (I.K.L.); vkachrimanidou@gmail.com (V.K.); kpapadaki@ionio.gr (A.P.); anthi18stam@yahoo.com (A.S.); ladakisdimitris@gmail.com (D.L.); eeriotou@ionio.gr (E.E.) **\*** Correspondence: kopsahelis@upatras.gr or kopsahelis@ionio.gr; Tel.: +30-26710-26505

**Citation:** Lappa, I.K.;

Kachrimanidou, V.; Papadaki, A.; Stamatiou, A.; Ladakis, D.; Eriotou, E.; Kopsahelis, N. A Comprehensive Bioprocessing Approach to Foster Cheese Whey Valorization: On-Site β-Galactosidase Secretion for Lactose Hydrolysis and Sequential Bacterial Cellulose Production. *Fermentation* **2021**, *7*, 184. https://doi.org/ 10.3390/fermentation7030184

Academic Editors: Giuseppa Di Bella and Alessia Tropea

Received: 10 August 2021 Accepted: 6 September 2021 Published: 8 September 2021

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**Abstract:** Cheese whey (CW) constitutes a dairy industry by-product, with considerable polluting impact, related mostly with lactose. Numerous bioprocessing approaches have been suggested for lactose utilization, however, full exploitation is hindered by strain specificity for lactose consumption, entailing a confined range of end-products. Thus, we developed a CW valorization process generating high added-value products (crude enzymes, nutrient supplements, biopolymers). First, the ability of *Aspergillus awamori* to secrete β-galactosidase was studied under several conditions during solidstate fermentation (SSF). Maximum enzyme activity (148 U/g) was obtained at 70% initial moisture content after three days. Crude enzymatic extracts were further implemented to hydrolyze CW lactose, assessing the effect of hydrolysis time, temperature and initial enzymatic activity. Complete lactose hydrolysis was obtained after 36 h, using 15 U/mL initial enzymatic activity. Subsequently, submerged fermentations were performed with the produced hydrolysates as onset feedstocks to produce bacterial cellulose (5.6–7 g/L). Our findings indicate a novel approach to valorize CW via the production of crude enzymes and lactose hydrolysis, aiming to unfold the output potential of intermediate product formation and end-product applications. Likewise, this study generated a bio-based material to be further introduced in novel food formulations, elaborating and conforming with the basic pillars of circular economy.

**Keywords:** cheese whey; *Aspergillus awamori*; β-galactosidase; lactose hydrolysis; *Acetobacter xylinum*; bacterial cellulose
