DBUVC ve UVCLED ışınlamanın kiraz ve vişne yüzeyinde mikrobiyel inaktivasyona ve meyve kalite özelliklerine etkisi
Effect of DBUVC and UVCLED irradiation on microbial inactivation and quality attributes on sweet and sour cherry surfaces
Yazar: AYŞENUR BETÜL BİLGİN
Danışman: PROF. DR. PERVİN BAŞARAN AKOCAK
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Gıda Mühendisliği Ana Bilim Dalı / Gıda Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Gıda Mühendisliği = Food Engineering
Dizin: Bakteriler-aerobik = Bacteria-aerobic ; Gıda ışınlaması = Food irradiation ; Meyve kalitesi = Fruit quality ; Mikroflora = Microflora ; Morötesi ışınlama = Ultraviolet irrigation ; Pseudomonas syringae = Pseudomonas syringae ; Sert çekirdekli meyveler = Stone fruits

Özet:
Ultraviyole – C (UVC), fiziksel bir yöntem olan ve genellikle gıdalarda dezenfeksiyon amaçlı kullanılan mor ötesi ışıktır. Son yıllarda, geleneksel düşük basınçlı UVC (DBUVC) lambaların ve son yıllarda yeni UVC kaynağı olarak kullanılan UVC – ışık yayan diyotların (light-emitting diodes, LED) (UVCLED) gıdalarda meyve ve sebze dezenfeksiyon çalışmaları yoğunluk kazanmıştır. Bu projede, UVC kaynağı olarak UVCLED ve DBUVC ışınlanmasıyla kiraz ve vişne yüzeyinin dezenfeksiyonun sağlanması ve meyvelerin raf ömrünün arttırılması hedeflenmiştir. 
Kiraz ve vişne yüzeyine daldırma ve spreyleme yöntemi ile Pseudomonas syringae, meyveden izole edilen maya inoküle edilmiştir. Meyve yüzeyinde doğal olarak bulunan toplam aerobik mezofilik bakteri (TAMB), toplam küf ve maya (TKF) ve inoküle edilen mikroorganizmalar hedeflenerek meyve yüzeyi 30 saniye, 3 ve 10 dakika UVCLED (200 – 260 nm) ve DBUVC (253,7 nm) ile ışınlanmıştır. Her iki UVC lamba ile ışınlanmış meyveler, 25-28˚C (%40-60 nem)'de ve +4˚C'de depolanarak mikroorganizmalardaki inaktivasyon etkisi periyodik olarak değerlendirilmiş ve ürünlerin raf ömrü incelenmiştir. Işınlama öncesi ve sonrası meyvelerde meydana gelen fizikokimyasal (meyve ağırlığı, pH, toplam çözünebilir katı madde miktarı, su aktivitesi, toplam fenolik madde miktarı, antioksidan aktivite ve renk) değişimler gözlenmiştir. Tüm bu sonuçlar ile UVCLED ve geleneksel DBUVC lambaların inaktivasyon etkinliği ve kalite üzerinde etkisi karşılaştırılmıştır. 3 ve 10 dakika DBUVC ışınlamanın, UVCLED'e göre, 30 saniye UVCLED ışınlamanın ise DBUVC'ye göre daha etkili olduğu tespit edilmiştir. Toplamda tüm sürelerde ve mikroorganizmalarda en düşük ve en yüksek inaktivasyon UVCLED ışınlama ile 0,31 – 0,86 kob/g, DBUVC ile 0,11 – 1,56 kob/g olarak gerçekleşmiştir. Hem kiraz hem de vişnede ışınlama öncesi ve sonrası toplam ağırlık, su aktivitesi, pH, toplam çözünür katı madde miktarı ve renk değerlerinde (L*, a*, b* ve H˚) önemli bir farklılık bulunmamıştır (p > 0,05). Vişnede UVCLED ışınlama ile fark edilebilir düzeyde (∆EUVCLED* = 1,17 – 3,30) renk değişimi tespit edilmiştir. Toplam fenolik madde ve antioksidan madde miktarında çoğunlukla önemli bir artış gözlemlenmiştir (p < 0,05). Işınlanmış meyvelerin +4 ve 25˚C'de depolanmasıyla raf ömrünün ortalama %30 oranında arttığı tespit edilmiştir. 
Sonuç olarak; DBUVC, UVCLED ışınlamaya göre genel olarak mikroorganizma inaktivasyonunda daha etkili olduğu, antioksidan aktivitesi ve toplam fenolik madde miktarının artması dışında meyvelerin fizikokimyasal özelliklerinde önemli bir etkisinin bulunmadığı tespit edilmiştir.

Abstract:
Sweet cherry (Prunus avium) and sour cherry (Prunus cerasus) are among the most important non-climacteric fruits of the Prunus genus from the Rosaceae family. They have about 83% water, low calories (63 – 61 kcal), high dietary fiber (1.70 – 3.16 g) and L-ascorbic acid (5.2 – 2.5 mg). They have substantial anthocyanins and antioxidant compounds. Besides, it is proven that they have beneficial effects for patients with diabetes and they've decreased cholesterol, inhibited carcinogenesis for colon cancer, and regulated sleep duration.
In 2020, Turkey produced 724,994 tons of sweet cherries and 189,184 tons of sour cherries. In the same year, having a share of 11% on a ton basis in the world's sweet cherry exports, Turkey ranks third-biggest sweet cherry exporter with 87,254 tons in the world ranking. Generally, economic losses occur due to microbial degradation during transportation. The average distance of countries of supply sweet cherries from Turkey is 1,699 km. Therefore, the fruit quality and its shelf life are very important criteria in exportation duration due to the perishable structure of sweet and sour cherries.
Pseudomonas syringae spp. causes bacterial cancer on the sprouts, flowers, branches, leaves, and fruits. Erwinia amylovora, Monilinia fructicola, Monilinia laxa, Wilsonomyces carpophilus, Penicillium expansum, Alternaria alternata, etc. microorganisms lead to pre-and post-harvest microbial deterioration in sweet and sour cherries.
In order to prevent losses, various techniques (chemical, physical and biological) are evaluated worldwide. Some examples are fumigation, cold treatment, modified atmosphere packaging (MAP), controlled atmosphere, edible films, bacteriophages, gamma irradiation, microwave, and other techniques. In the last two decades, UVC light is the most promising technique on fruits and vegetables surface treatment.
Ultraviolet – C (UVC) is a physical technique, which has germicidal effects on microorganisms, that is generally used for disinfection in foods, especially fruits and vegetables surfaces and juices. Microorganisms such as Escherichia coli, Salmonella enterica, Salmonella entiridis, Listeria monocytogenes, Staphylococcus aureus, Bacillus subtilis from bacteria, Penicillium expansum, Aspergillus niger from mold, Zygosaccharomyces rouxii from yeast, and MS2, ΦX 174 ve Qβ from viruses were inactivated up to 6 log by UVC (250 – 280 nm) irradiation of food such as water, juices, fruits and vegetables such apple, grape tomato, lettuce leaves, litchi, longan, rambutan, etc. As a consequence of UVC irradiation, no significant difference physical and chemical changes were observed in research.
Sun is a natural sources, low pressure and medium pressure mercury vapour lamps, pulsed xenon lamps, excimer, fluorescent lamp are artificial sources of UVC light. Light emitting diodes (LED) is a novel sources of UVC, UVB, and UVA sources. It has many advantages than the other UVC sources such as robust structure, non-toxic, working at low temperatures, long life, small size and cheap.
Traditionally low-pressure UVC (LPUVC) lamps are being used and in recent years, novel UVC light-emitting diodes (UVCLED), which have been tested for the disinfection of foods. In this study, it is aimed to provide disinfection on the surface of cherries and sour cherries and to increase the shelf life of the fruits with UVCLED and LPUVC irradiation. 
Sweet and sour cherries were purchased from local markets and bazaars. P. syringae spp. and yeasts isolated from fruits were inoculated by dipping and spray inoculation techniques. Then, fruits were irradiated by UVCLED (200 – 260 nm) and LPUVC (253.7 nm) for 30 seconds, 3, and 10 minutes for inactivation of P. syringae spp., yeasts, naturally found microorganisms (total aerobic mesophilic bacteria (TAMB) and total mold and yeast (TMY). Before and after irradiation, physicochemical and microbiological analyses were performed. Irradiated fruits were stored at 25 – 28 ˚C (40 – 60 humidity) or +4˚C, and the inactivation effect on these microorganisms was evaluated. Before and after irradiation, physicochemical properties of fruits (weight, pH, total soluble solids, water activity, total phenolic content, antioxidant activity, color) and microbiological changes were observed.
3 and 10 minutes of LPUVC irradiation was more effective than UVCLED, and 30 seconds of UVCLED irradiation was more effective than LPUVC. In general, at all irradiation durations and all microorganisms, the lowest and highest inactivation was 0.31 – 0.86 CFU/g with UVCLED irradiation and 0.11 – 1.56 CFU/g with LPUVC irradiation. The highest inactivation occurred on TMAB (1.56 log) on the surface of fruits irradiated with LPUVC for 10 minutes. The lowest inactivation (0.11 log) was observed in yeasts inoculated on the surface of sweet and sour cherries irradiated with LPUVC for 30 seconds. Both UVCLED and LPUVC light treatments showed a higher reduction of the natural microflora (total bacteria, mold, and yeast) of the sweet and sour cherries compared to the inoculated microorganisms (P. syringae spp. and yeast). So, it has been observed that P. syringae spp. and yeasts are more resistant compared to natural microflora and TAMB are more resistant compared to TMY (for 30 second and 3 minutes irradiation).
There was no significant difference in total weight, water activity, pH, total soluble solids content, and color values (L*, a*, b*, and H˚) before and after irradiation in both sweet cherry and sour cherry (p > 0.05). Sour cherries with UVCLED irradiation showed a slightly noticeable (∆EUVCLED* = 1.17 – 3.30) color change. It was observed that the total amount of phenolic substances and antioxidant activity mostly increased by 73 – 113% and 77 – 102%, respectively. It was determined that the shelf life of irradiated fruits extended by 30% on average within 11 – 22 days of storage at +4 and 25˚C. Bacteriophage was isolated against P. syringae spp. as a host, but could not be identified.
In conclusion, P. syringae spp., yeasts, TAMB, and TMY were inactivated by both irradiation treatment and the shelf life of sweet and sour cherries was extended. But, LPUVC was found to be more effective than UVCLED irradiation in terms of microbial inactivation. It was determined that there was no significant effect on the physicochemical properties of fruits, except for the increase in total antioxidant activity and total phenolic content.