Artan dünya nüfusu ile birlikte besin ihtiyacını karşılamada çıkan sorunlar gıda katkı maddelerine ilgiyi arttırmıştır. Bir tür gıda katkı maddesi olarak gıda koruyucularının güvenli kullanımı da giderek daha fazla dikkat çekmektedir. İzin verilen bileşen ve kullanım konsantrasyonları ülkeden ülkeye farklılık gösterse de potasyum sorbat (PS) Amerikan Gıda ve İlaç Dairesi'nin güvenli koruyucular listesinde kabul edilmektedir. Maya ve küf engelleme özelliği sayesinde neredeyse tüm hazır gıda ve unlu mamullerin içeriğinde bulunan potasyum sorbatın insan vücuduna günlük alım miktarına dikkat edilse de suda çözünme özelliği nedeniyle kontrolsüz bir şekilde üretimden kaynaklı oluşan atık sularla birlikte sucul ekosistemde yaşayan canlılar üzerinde tehdit oluşturmaktadır. Bu durumda sucul ekosistemlerde birincil üretimde önemli bir yere sahip olan prokaryotik mavi-yeşil alglerde strese bağlı olaylar nedeniyle hasarlar oluşabilmektedir. Yapılan bu çalışmada, potasyum sorbat bileşiğinin Arthrospira platensis alginin klorofil-a, OD 560 ve kültür ortamı pH değerlerinde oluşturduğu değişimler ile birlikte antioksidan parametrelerinde meydana getirdiği cevaplar incelenmiştir. Bu amaçla, A. platensis algi kültürleri 3 tekrarlı olacak şekilde farklı konsantrasyonlarda (100, 200, 300, 400, 500 ve 600 ppm) potasyum sorbat bileşiğine 10 gün boyunca maruz bırakılmış, klorofil-a ve OD 560 değerlerindeki değişim günlük olarak ölçülmüştür. Kültür ortamı pH değerlerindeki değişim karanlık periyodun son saatinde (saat 08:00) ve aydınlık periyodun son saatinde (saat 20:00) olmak üzere günde iki defa 10 gün boyunca ölçülmüştür. Antioksidan parametrelerdeki değişimlerin belirlenmesi için 10. günün sonunda kültürlerden pelletler alınmıştır. Bu pelletler üzerinden algin prolin, hidrojen peroksit (H2O2), malondialdehit (MDA) miktarlarındaki ve glutatyon redüktaz (GR), süperoksit dismutaz (SOD), askorbat peroksidaz (APOD) gibi antioksidan enzimlerinin aktivitelerindeki değişimler incelenmiştir. Çalışmada, potasyum sorbat bileşiğine maruz bırakılan A. platensis alginin OD 560 ve klorofil-a değerlerinde konsantrasyon artışına ve zamana bağlı olarak kontrole göre 7. günden itibaren azalma gözlenmiştir. Sadece 100 ppm konsantrasyonda kontrole göre istatistiksel bir değişim gözlenmemiştir. Kültür ortamı pH değerleri 6. gün aydınlık periyodun son saatinden (saat 20:00) itibaren 200, 300, 400, 500 ve 600 ppm konsantrasyonlarda azalmaya başlamış, 9. günden itibaren tüm konsantrasyonlarda kontrole göre azalma görülmüştür. SOD aktivitesi kontrole göre 100 ve 500 ppm hariç diğer tüm konsantrasyonlarda istatistiksel olarak azalma gösterirken, GR aktivitesi 100 ppm hariç diğer tüm konsantrasyonlarda azalma göstermiştir. Prolin miktarında sadece 500 ppm konsantrasyonunda azalma görülürken, diğer tüm konsantrasyonlarda istatistiksel olarak anlamlı artma tespit edilmiştir. APOD aktivitesinde, H2O2 ve MDA miktarlarında kontrole göre bir değişim gözlenmemiştir. Ortaya çıkan sonuçlarda potasyum sorbatın A. platensis alginin gelişimi üzerine olumsuz etki ederek metabolikdengeyi değiştirdiği saptanmış, prokaryotik alglerde toksik etkileriyle ilgili ipuçları elde edilmiştir.
With the increasing world population, the problems in meeting the nutritional needs have increased the interest in food additives. The safe use of food preservatives as a type of food additive is also getting increased attention. The food additives in question are generally defined as "substances used to affect the properties of foods in the desired way". These properties include storage life, appearance and flavor. Potassium sorbate is one of the most widely recognised and used food additives. Potassium sorbate (E-202) is accepted on the US Food and Drug Administration's list as a safe preservative, although the permitted ingredients and usage concentrations vary from country to country. It has white colour, soft, odourless and shiny appearance. It is easy to dissolve in water. Although potassium sorbate is preferred at many points, it has been developed especially for liquid stock solutions. Although attention is paid to the daily intake of potassium sorbate to human body, which is in the content of all ready-made foods and bakery products due to its yeast and mold inhibition feature, studies have been carried out that it causes toxic effects both in humans and other living things. Moreover, it poses a threat to organisms in the aquatic ecosystem with the wastewater resulting from uncontrolled excretion due to its water-soluble feature. In addition to food additives that are mixed into aquatic ecosystems due to unconscious waste management during and after the production phase in the industry, these substances are somehow contaminated to aquatic ecosystems directly or indirectly as a result of the use of foodstuffs by humans. In this case, damage may occur due to stress-related events in prokaryotic blue-green algae, which have a key place in photosynthesis production in the aquatic ecosystem. Algae, which are very quickly affected by the changes that may occur in the ecosystem, respond rapidly to favourable and unfavourable conditions in the environment. Since there are changes in the amount of biomass, photosynthesis and reproductive capacity of the organism, species distributions in the algal community of the aquatic ecosystem can be affected. Moreover, highly structured organisms at the top of the food chain are also affected by these changes. Therefore, algae are an extremely important group of organisms used to investigate the effects of chemicals that may be harmful to the environment. In this study, the changes in the chlorophyll-a and OD 560 values, pH values of the culture medium and antioxidant parameters of Arthrospira platensis algae were investigated for the potassium sorbate compound. A. platensis (M2) algae obtained from Soley Microalgae Institute was cultured under axenic conditions in the Plant Physiology and Algal Ecology laboratory of Sakarya University Biology Department. Potassium sorbate (C6H7KO2) chemical used in the study was obtained from commercial suppliers. During the study period, A. platensis algae cultures were exposed to potassium sorbate compound at different concentrations (100, 200, 300,400, 500 and 600 ppm) for 10 days in 3 repetitions, and the daily changes in chlorophyll-a and OD 560 values were measured. The change in pH values of the culture medium was measured twice a day for 10 days, at the last hour of the dark period (08:00) and at the last hour of the light period (20:00). Pellets were taken from the cultures at the end of the 10th day to determine the changes in antioxidant parameters. The changes in the amounts of malondialdehyde (MDA), hydrogen peroxide (H2O2), proline, and the activities of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) were investigated on these pellets. Different modified methods were used to determine enzyme activities and other antioxidant parameters, and measurements were made spectrophotometrically. One-way analysis of variance (ANOVA) was performed on the data and LSD test was applied to determine the difference between the variables using the SPSS 20.0 program. In the study, addition of potassium sorbate to the culture medium of A. platensis for 10 days significantly decreased both OD 560 and chlorophyll-a values from the 7th day compared to the control in a dose dependent manner. No statistical change was observed at 100 ppm concentration compared to the control. The pH values of the culture medium started to decrease at 200, 300, 400, 500 and 600 ppm concentrations from the last hour of the bright period (20:00) on the 6th day, and a decrease was observed in all concentrations from the 9th day compared to the control. SOD activity decreased statistically at all concentrations except 100 and 500 ppm, while GR activity decreased at all concentrations except 100 ppm compared to control. While a decrease was observed in the amount of proline only at 500 ppm concentration, a statistically significant increase was found at all other concentrations. No change was observed in APX activity, H2O2 and MDA amounts compared to control. It was concluded that potassium sorbate compound negatively affected the OD 560 (indicator of development), and chlorophyll-a and pH values (indicators of photosynthetic activity) of A. platensis algae. Moreover, the antioxidant responses to potassium sorbate applied to A. platensis showed that potassium sorbate had toxic effects. The changes in enzyme activities and an increase in the amount of proline can be considered as proof that potassium sorbate affects the metabolic balance in the cell. Although it was determined that the inhibitory effect appeared much earlier in similar studies with different chemicals, the negative effect of potassium sorbate on growth and photosyntetic activity appeared from the 7th day in this study. It was also considered that the devastating effect of 100 ppm was lower than the other doses used in the study. Moreover, the doses applied to this prokaryotic blue-green algae were lower than those applied to other eukaryotic algae in other studies. This finding indicated that prokaryotic algae may be more sensitive to potassium sorbate compound. The necessity of keeping the food additives under control, which is used extensively in the food and pharmaceutical industry has emerged once again. As shown in our study, other studies have also shown the toxic effect of these kind of chemicals on different algae, other living organisms such as zebra fish, invertebrates, and humans. It is seen that it is extremely necessary to limit the consumption of food additives and to follow up the resulting wastes. The use of these small organisms in the detection of environmental pollution caused by food additives and especially potassium sorbate compound will shed light on future studies as fast and reliable indicators. Increasingthe number of such studies will also be important in terms of providing scientific data for future toxicology studies on algae with different chemicals.
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