# Microbial Application to Improve Olive Mill Wastewater Phenolic Extracts
## 3 Discussion  
Crude OMW was sampled from a collection tank during a continuous oil extraction from different olive cultivars. The sample showed a pH value of 4.8, within the range of 2.2-5.9 as reported by [PERSON] et al. [5], and close to those reported by [PERSON] et al. [6] and [PERSON] et al. [18] who found values between 4.5 and 5.16 for OMW from the three-phase extracting system. Here, the dry matter value was slightly lower than those reported by the previous authors, as a consequence of sample pre-treatment, namely centrifugation and filtration. The total phenols were also lower than those discussed by [PERSON] et al. [29] who found value of 6.46 g/L in effluent generated from the three-phase extraction system. The amount of 1.34 g/L detected in the present work was comparable to 1.8 g/L reported by [PERSON] [18] and within the range 0.03-6.13 g/L reported by [PERSON] et al. [30]. The variability in total phenol concentration may be attributed to several factors, such as the olive cultivars and their degree of ripening. Moreover, the agronomic conditions and treatments applied to extract the olive oil and to treat the OMW, may also significantly impact the quantitative and qualitative phenolic content and solid residues of OMW [5, 31]. The major compounds detected in OMW are HT and TY, with HT known for its high antioxidant activity [32]. [PERSON] et al. [5] in their review reported that in OMW, HT is found in the range of 20-1224 mg/L, while TY is between 145-208 mg/L. Regarding OLE, it has not been detected in OMW deriving from late-harvest olives [31], and its content has been described as highly variable [11, 29, 33]. The solid phase recovery of polyphenols from OMW has been successfully proposed using adsorbent resins, particularly with the S-DVB-based resins [14, 15, 34]. In the present work, in order to optimize the process, different resins, including the SP207, never employed before in the recovery of phenolic compounds from OMW, were tested. All the tested resins were capable of successfully adsorbing polyphenols [34, 35], with the SP207 resin showing a high and selective affinity for OMW polyphenols. This non-polar resin, generally used for the recovery of phenolic compounds from citrus, apple, and winery by-products and wastes [36, 37, 38], showed the best efficiency in terms of total phenols concentration and selective recovery of the main OMW bioactive compounds. This type of approach to the recovery of bioactive compounds from OMW is desirable for the scale-up  
Figure 2: Concentration of hydroxytyrosol, tyrosol, and oleuropein after bioconversion of diluted OMW extract by Lallzyme, extracellular broths and pellets of the two tested strains after 2 h at 50 \({}^{\circ}\)C. Different letters indicate statistical differences among the columns of the same compound (Significance at \(p<0.001\)). from laboratory to industrial production thanks to the simple and reproducible operating conditions and to the low costs of the process. The enzymatic activity, as expected, highlighted the absolute supremacy of the _A. niger_ strain, confirming its successful employment at an industrial level to produce purified enzymes [11]. The hyphal mode of fungal growth and its robustness to a wide range of pH and water activity make fungi extremely efficient in the bioconversion of solid substrates [39]. In fact, live _A. niger_ culture showed an enzymatic activity up to 45-fold higher than the commercial enzyme. The _W. anomalous_ and _L. plantarum_ tested strains gave interesting results. In particular, _W. anomalous_ showed a beta-glucosidase activity statistically equal to that of the commercial enzyme, and an esterase value higher than that of the commercial enzyme. Despite its potential to produce enzymes of technological importance, _W. anomalous_ has been scarcely explored in food and byproduct applications. The interest in microbial enzymes for biotechnology applications has grown above all in the bioconversion of industrial by-products [40].