Olive Mill Waste Seen as a Renewable Resource for Biosurfactant Production

The Mediterranean region, includ­ing Spain, Italy, Greece and Tunisia, pro­duces the vast major­ity of world’s olive oil which con­se­quently gen­er­ates large amounts of pol­luted waste dur­ing the pro­duc­tion process.

Researchers are actively seek­ing strate­gies to reduce the vast quan­ti­ties of olive mill byprod­uct that is both envi­ron­men­tally and eco­nom­i­cally viable. Spain as the largest pro­ducer of olive oil has been espe­cially focus­ing efforts on low­er­ing this waste bur­den and its impact on the envi­ron­ment.
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During the extrac­tion phase, a paste known as alpe­orujo or olive mill waste (OMW) is pro­duced. This solid waste is a rich source of polyphe­nols which exhibit antimi­cro­bial activ­ity and thereby inhibit fur­ther bio­log­i­cal recy­cling. Currently, alpe­orujo is used for energy pro­duc­tion which is not pro­duc­tive or cost-effec­tive.

Alpeorujo also has high amounts of lig­no­cel­lu­losic mate­r­ial, resid­ual oil and min­er­als suit­able as a car­bon source for bac­te­ria growth.

Biosurfactants (BS) are bio­log­i­cal and biodegrad­able sur­face active mol­e­cules pro­duced through fer­men­ta­tion into var­i­ous chem­i­cal struc­tures such as gly­col­ipids, fatty acids and phos­pho­lipids. They are also supe­rior alter­na­tives to syn­thetic sur­fac­tants due to opti­mal sta­bil­ity and per­for­mance under extreme envi­ron­men­tal con­di­tions.

The use of these com­pounds in soil con­di­tion­ing, food, med­i­cine and phar­ma­ceu­ti­cal indus­tries have fur­ther added infi­nite value as an envi­ron­men­tally viable replace­ment to the chem­i­cally pro­duced sur­fac­tants.

However, the high devel­op­ment costs are a draw­back on the large-scale indus­trial pro­duc­tion of bio­sur­fac­tants and con­sid­er­able process opti­miza­tion is required to ensure eco­nomic sus­tain­abil­ity.

One strat­egy employed by agri­cul­ture and food indus­tries is to use waste prod­ucts such as waste oils, fatty acids and glyc­erol as a car­bon source by fer­men­ta­tion to reduce asso­ci­ated pro­duc­tion costs.

This idea led a col­lab­o­ra­tive group of researchers from Spain and Ireland to the inno­v­a­tive use of car­bon-rich alpe­orujo in the pro­duc­tion of bio­sur­fac­tants through fer­men­ta­tion sub­strates Pseudomonas aerug­i­nosa and Bacillus sub­tilis bac­te­r­ial species.

In a ground­break­ing twist, the same research groups demon­strated that hydrol­y­sis pre­treat­ment of the OMW sig­nif­i­cantly increased bioavail­abil­ity of the sug­ars present in alpe­orujo result­ing in marked improve­ment in bio­sur­fac­tants pro­duc­tion.

The sci­en­tists found that com­pared to acid or acid-enzy­matic pre­treat­ment, the high­est yield of sur­fac­tant was pro­duced by enzy­matic hydrol­y­sis pre­treat­ment of the waste by-prod­uct.

The group also showed that the use of OMW as the sole car­bon source is sim­i­lar to that of glu­cose for bio­sur­fac­tant pro­duc­tion, indi­cat­ing large scale BS pro­duc­tion achiev­able at a lower cost and a more effi­cient sub­strate.

Furthermore, the pro­duc­tion of bio­sur­fac­tants was not only sig­nif­i­cantly improved with increased con­cen­tra­tion of OMW, but there was also a faster turn-around with the hydrolyzed pre­treat­ment process.

The sci­en­tists con­cluded that ​“an appro­pri­ate hydrol­y­sis pre­treat­ment is a key fac­tor for a poten­tial indus­trial pro­duc­tion of bio­sur­fac­tant from OMW.”

The researchers noted that ​“while many agroin­dus­trial residues demand some kind of phys­i­cal pre­treat­ment before the hydrol­y­sis stage, OMW is already ground, so its use will avoid this energy-inten­sive step. This imparts a great advan­tage over other lig­no­cel­lu­losic agroin­dus­trial wastes in a future devel­op­ment of a cost effec­tive BS pro­duc­tion process.”

• Ramírez, Ignacio Moya, et al. ​“Rhamnolipid and sur­factin pro­duc­tion from olive oil mill waste as sole car­bon source.” Bioresource tech­nol­ogy 198 (2015): 231 – 236


• Ramírez, Ignacio Moya, et al. ​“Hydrolysis of olive mill waste to enhance rham­no­lipids and sur­factin pro­duc­tion.” Bioresource tech­nol­ogy 205 (2016): 1 – 6