Düşük proteinli süt-bazlı fermente bir ürün geliştirilmesi
Development of milk-based fermented product with low protein content
Yazar: SİNEM BETÜL CANİKLİ
Danışman: PROF. DR. MERAL KILIÇ AKYILMAZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Gıda Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Gıda Mühendisliği = Food Engineering

Özet:
Fermente süt ürünleri, laktik asit üreten kültürler tarafından fermente edilen ürünlerdir. Yoğurt gibi fermente süt ürünleri protein, kalsiyum, süt yağı, potasyum, magnezyum, B2, B6 ve B12 vitaminlerince zengindir. Laktik asit bakterileri ile fermente edilen ürünlerin sağlığa olumlu etkileri bilinmektedir. Bu çalışmada, başta fenilketonüri hastaları olmak üzere, diğer benzer metabolik rahatsızlıklar ve protein alerjisine sahip tüketicilere yönelik olarak süt-bazlı fermente bir ürün geliştirilmesi amaçlanmıştır.
Fenilketonüri, fenilalanin hidroksilaz enzimini [EC 1.14.16.1] kodlayan gende meydana gelen mutasyonlardan kaynaklanan, otosomal resesif kalıtsal metabolik bir rahatsızlıktır. Bu enzim, fenilalaninin karaciğerde tirozine dönüşümünü gerçekleştirir. Enzim düzeyindeki azalma ve/veya enzim aktivitesindeki düşüş, kan ve doku fenilalanin konsantrasyonlarında kalıcı artışa neden olur ve bu artış özellikle beyin için toksik etkidedir. Geç teşhis ve/veya uygun olmayan diyetle beslenen hastalarda zihinsel bozukluk, gelişimsel yavaşlama, ilerleyici düşünsel bozukluk, nöbetler, dikkat eksikliği/hiperaktivite, otonomide azalma, saldırganlık, endişe ve sosyal izolasyon gibi davranış problemleri görülebilir. Fenilketonüri hastalarına yönelik ürün geliştirirken fenilalanin miktarı dikkate alınmalı, ürün duyusal özellikleri açısından kabul edilebilir olmalı ve depolama süresinde dayanıklılığı sağlanmalıdır.
Geliştirilen üründe yoğurtta bulunan laktik asit miktarı ve fenilketonüri hastalarının tüketebileceği fenilalanin içeriği esas alınarak süt bazı olarak uygun oranda yağsız süttozu ve yayıkaltı suyu tozu kullanılmıştır. Üründe uygun yapının ve yapısal dayanıklılığının sağlanması için patates nişastası, ksantan gam ve keçiboynuzu gamı kullanılmıştır. Öncelikle ürünün üretim yöntemi ön denemelerle belirlenmiştir. Üretimde ilk aşamada süt bazının laktik asit bakterileri ile fermentasyonu gerçekleştirilmiş, ikinci aşamada fermente süt bazı sıcak suda çözündürülen nişasta ve gam karışımı ile karıştırılmış ve son aşamada ürün 4C'ye soğutulmuştur. Ürün için optimum formülün bulunması için patates nişastası, ksantan gam ve keçiboynuzu gamı oranları faktör olacak şekilde tepki yüzey yöntemi uygulanarak üç seviyeli, merkezi kompozit deneme desenine göre üretimler yapılmıştır. Üretimden bir gün sonra örneklerin pH, titrasyon asitliği, serum ayrılması, su tutma kapasitesi, reolojik ve tekstürel özellikleri ölçülmüştür.
Örneklerin pH değerinin 1 gün depolama sonrasında formüle göre değişmediği saptanmıştır. Titrasyon asitliği patates nişastası arttıkça artmış, keçiboynuzu gamı arttıkça azalmıştır. Örneklerde kendiliğinden serum ayrılması saptanmamıştır. Ürünün su tutma kapasitesinde nişasta ve keçiboynuzu gamı ilavesi ile artış gözlenmiştir. Görünür viskozite değeri üzerinde her üç bileşenin etkisinin pozitif olduğu saptanmıştır. Nişasta ve keçiboynuzu gamı artışı örneklerin kıvam katsayısını arttırmıştır. Örneklerin akma gerilimi nişasta ve ksantan gamı ilavesinden pozitif yönde etkilenmiştir. Elastik modül (G') değeri de görünür viskozite değeri gibi her üç bileşenden pozitif yönde etkilenmiştir.
Elde edilen sonuçlara göre optimum formülün bulunması için akma gerilimi, kıvam katsayısı ve su tutma kapasitesi hedef değerleri kullanılmıştır. Optimum hedef değerleri sağlayacak üç formül belirlenmiştir. Optimizasyondan elde edilen üç formül ile üretilen ürünlerin yapısal özellikleri ölçülerek tahminlenen değerlerin doğrulaması yapılmıştır. Ayrıca bu üç ürün duyusal analize tabi tutularak yapı, tat ve tüketici kabul edilebilirliği belirlenmiştir. Üç ürünün de parçacık büyüklüğü hariç benzer özelliklere sahip olduğu ve kabul edilebilir oldukları tespit edilmiştir.

Abstract:
Fermented milk products are produced by fermentation of milk with lactic acid bacteria. Fermented milk products such as yoghurt contain lots of health-beneficial components such as calcium, potassium, magnesium, protein, milk fat, vitamin B2, B6 and B12. Besides these, it is also considered as a carrier of probiotic bacteria to human body. In this study, it is aimed to produce a milk-based fermented milk product for consumers with phenylketonuria, metabolic diseases and protein allergy.
An impaired activity of phenylalanine hydroxylase (PAH; EC 1.14.16.1) leads to phenylketonuria (PKU) . PAH is an enzyme that is in charge of conversion of phenyalanine (PA) to tyrosine. While doing that it needs BH4 and dioxygen presence. This enzyme activity disorder is caused by the mutation in the gene that is responsible for the secretion of the enzyme. The conversion of PA is important because it is helpful for the formation of neurotransmitters such as serotonin and dopamin, which may affect the happiness of humankind and prevention the accumulation of metabolites such as phenylpyruvic acid.
When the blood level of PA is high, it leads to other amino acids to become limited from the rate point of view because it competes with the other large amino acids which are part of transportation system to traverse the blood-brain barrier. Untreated PKU negatively affects the normal brain development and causes some symptomps such as epilepsy. More severe neurological disorders, mental retardation, slow growth, seizures, attention deficit/hyperactivity, aggression, anxiety and social isolation could result in patients that are late-diagnosed or fed with unsuitable diet. These risks of the disorder are prevented by neotanal screening programs and early treatment. The prevelance of the illness all around the world can be vary by the genetical factors. For example this ratio is 1:4500 in Ireland while the ratio is 1:2600 in Turkey. The high possibility of the occurance of PKU in Turkey is due to the consanguineous marriages.
PKU patients need to consume PA-restricted diet throughout their life. When a food product is developed for PKU patients, the amount of phenylalanine should be considered. In addition, the product should have acceptable sensory properties and it should be stable during storage time.
In this study, a milk-based fermented milk product was developed for consumers with PKU. Required amounts of nonfat milk powder and buttermilk powder were determined by considering the amount of lactic acid and the amount of phenylalanine that could be consumed by the patients. For obtaining a suitable structure and stability, potato starch, xanthan gum and locust bean gum were used. Production method was determined by preliminary experiments. In the first stage of production, milk base was fermented by using lactic acid bacteria and in the second stage, resulting fermented base was mixed with starch and gum mixture. At the last stage, product was cooled to 4C. For determining optimum formula, a face-centered central composite design with three levels and blocks was used in response surface method by taking the proportion of potato starch, xanthan gum and locust bean gum as factors. The samples were prepared according to the experimental design with seventeen runs with production time as the blocks. pH, titratable acidity, serum separation, water holding capacity, rheological and textural properties of the samples were measured after one day of storage at 4C.
Rheological properties of the samples were determined by fitting flow curve data to the Herschel-Bulkley model. Yield stress, consistency coefficient and flow behavior index were calculated from the model by nonlinear regression. Thixotropy of the samples was determined by calculating the area between up and down flow curve. In addition, elastic (G') and viscous (G'') modulus of the samples were measured by a oscillatory stress sweep. Stress at which the G'' becomes higher than G' was determined as crossover stress.
All three components, potato starch, xanthan gum and locust bean gum, were found to be influential on the physicochemical and structural properties of the fermented product except pH and spontaneous serum separation.
Apparent viscosity of the product was positively affected by all components of the formula. Consistency coefficient of the samples was increased by levels of starch and locust bean gum.
Yield stress was positively affected by starch and xanthan gum. Values of G' increased by the increase in all components of the formula similar to apparent viscosity.
pH values of the samples measured after one day of storage were not changed according to the formula. Titratable acidity was increased by the increase in level of starch and decrease in level of locust bean gum.
Spontaneous serum separation was measured in samples stored in graduated tubes at 4C. Water holding capacity was determined by centrifuging a certain volume of the samples. There was no spontaneous serum separation in all samples. Water holding capacity of the product was enhanced by increase in the levels of starch and locust bean gum.
At the second stage of statistical analysis, optimization of the formula that would yield the best structural properties for fermented product was performed. Optimum formula was seeked based on the obtained results and taking yield stress, consistency coefficient and water holding capacity as the targeted properties. Target values of consistency coefficient and yield stress were determined according to the values measured in stirred yoghurt. Target water holding capacity was chosen to be maximized in the optimization. Three formula were chosen among twenty formulas that were estimated to have targeted values for selected properties provided by the statistical program.
For validation of the results of the optimization, samples were produced according to the three optimum formulas. Targeted properties including yield stress, consistency coefficient and water holding capacity of them were measured for validation of the estimations. Measured values of the samples were found to be close to the estimated values by the programconfirming the optimum formulas.
Sensory properties of the three optimum formulas were determined according to the descriptive sensory analysis method. Texture (color, particulated structure, particle size, consistency, spoonability, adhesiveness and slimeness) and flavor (sourness, milk fat flavor, foreign flavor, leftover flavor) properties were judged by panelists on a five-point scale. Samples were found to be similar in terms of textural and taste attributes. Only particle size was found to be different among the samples. All the samples were found to be acceptable by the panelists in terms of sensory properties.