پديد آورندگان :
پورعطا، رحمت اله دانشگاه زنجان - گروه شيمي، زنجان، ايران , جهانگير اصفهاني، حميد دانشگاه زنجان - گروه علوم و صنايع غذايي، فناوري مواد غذايي، زنجان، ايران , شهابي قهفرخي، ايمان دانشگاه زنجان - گروه علوم و صنايع غذايي، فناوري مواد غذايي، زنجان، ايران
كليدواژه :
آب گريزي , اسيد اولئيك , نشاسته , نانو TiO2 , UV , بسته بندي مواد غذايي
چكيده فارسي :
در ميان پليمرهاي زيست تخريب پذير، استفاده از نشاسته به علت قيمت ارزان و دسترسي آسان از اهميت به‌سزايي برخوردار است، اما به علت مقاومت كم و آبدوستي زياد در اين بيوپليمر، هنوز استفاده از آن در صنعت بسته‌بندي عملياتي نشده است. هدف از اين پژوهش، اصلاح ويژگي‌هاي آبدوستي و مكانيكي فيلم نشاسته با استفاده همزمان از اسيد اولئيك، نانو دي‌اكسيد تيتانيوم (TiO2) و پرتو فرابنفش (UV-C) بود. در اين پژوهش، محلولِ نشاسته- اسيداولئيك- TiO2 تهيه؛ و به‌منظور بهبود خصوصيات كاربردي آن، اين محلول در بازه‌هاي زماني (صفر، 30، 60 و 90 دقيقه) توسط پرتوUV-C اصلاح گرديد، سپس فيلم آن به روش قالب‌گيري محلول تهيه شد. جهت بررسي خصوصيات كاربردي فيلم در بسته‌بندي مواد غذايي ضخامت، مقاومت مكانيكي، زاويه تماس، نفوذپذيري نسبت به بخارآب، جذب رطوبت، محتواي رطوبت و حلاليت فيلم‌ها مورد بررسي قرار گرفتند. آزمون‌ها در قالب طرح كاملا تصادفي اجرا، و نتايج آن به روش دانكن مورد مقايسه قرار گرفتند. نتايج نشان دادند، كه با افزودن اسيد اولئيك و TiO2 به محلول نشاسته، زاويه تماس به‌طور قابل‌ملاحظه‌اي از 26/72 به 34/90 درجه افزايش و نفوذپذيري نسبت به بخارآب و جذب رطوبت فيلم‌هاي نشاسته‌اي كاهش مي‌يابد. در مطالعه خواص مكانيكي نيز مشاهده شد كه با افزودن اسيد اولئيك و TiO2، مقاومت كششي و الاستيسيته كاهش و كشش‌پذيري و انرژي كششي تا لحظه پاره شدن افزايش يافته است. با اعمال پرتودهي در بازه زماني كوتاه‌مدت (30 دقيقه)، تمامي پارامترهاي مربوط به خواص مكانيكي افزايش، و حلاليت به آب و جذب رطوبت فيلم‌هاي نشاسته‌اي كاهش يافتند. به‌نظر مي‌رسيد، استفاده همزمان از UV-C و TiO2 باعث بهبود اثر پرتو UV-C جهت ايجاد اتصالات عرضي در ماتريس بيوپليمر به صورت نشاسته- نشاسته و نشاسته- اسيد اولئيك شود؛ با اين حال، استفاده از TiO2 باعث تشديد اثر پرتوي UV-C و تسريع تغييرات آن در بازه زماني كوتاه‌تري (30 دقيقه) شد. به‌طور كلي به‌منظور بهبود خاصيت آبگريزي وخواص مكانيكي فيلم نشاسته، استفاده از اسيد اولئيك و TiO2 به‌صورت توأم بهترين نتايج اين پژوهش را در برداشته است. از اين رو يك گام رو به جلو براي استفاده صنعتي از نشاسته در بسته‌بندي مواد غذايي به حساب مي‌آيد.
چكيده لاتين :
Introduction: Among the bio-based materials which used in the food packaging, starch is interested as an ecofriendly material. This interest is mainly due to its acceptable film forming properties, easy access, renewability and low cost.
Nevertheless, high hydrophilic and weak mechanical properties have been limited its utilization as a commercial
packaging material. Many researches have been done to reduce hydrophilic properties of starch using chemical
modification, irradiation, and composition with nanoparticles and other biopolymers. Most of the methods are based on
blocking the hydroxyl groups of starch chains with hydrophobic agents, formation of emulsions and blocking of the pores.
Fatty acids, such as oleic acid (OA) are lipid derivatives that can potentially improve the moisture barrier properties of
hydrophilic films. OA is a yellow liquid at room temperature and miscible with biopolymer without further heating
treatment. Due to the polar nature of biopolymers, OA needs to surfactant to get homogenous distribution in the matrix
of biopolymers. On the other hand, OA is not very sensitive to oxidation which increases its safety in food packaging
applications. Titanium dioxide (TiO2) is an inert, cheap and nontoxic material with broad application as a food pigment
and potential activity against a wide variety of microorganism due to its photocatalytic activity.TiO2 is the most commonly
used semiconductor, photocatalyst which activated by UV ray. The main purpose of the current study was modification
of starch hydrophilicity using OA, nano-titanium dioxide and UV ray. In this study OA and TiO2 added at the optimized
condition and the solution was irradiated by UV ray. Materials and Methods: A starch solution 5 (wt. %) in distilled water was prepared. This solution was mixed and
heated (85 ˚C for 15 min) until the starch gelatinized. Thus, plasticizer (glycerol, 40 wt. % of dry base) was incorporated
into the solution to achieve more-flexible films. OA 1(wt. % of dry base) mixed with Tween 80 as emulsifier (10 wt. %
of the OA). This solution was mixed and heated (50 ˚C for 10 min). Then, 10 ml of distilled water was added to the
solution, and homogenized by ultrasonic homogenizer (Dr. Hielscher, Teltow, Germany) for 7 min. The suspension of
TiO2 nanoparticles in water was prepared so that the final TiO2 content in film specimens was 2 (wt % of dry base). The
suspensions were stirred for 10 min, and homogenized by ultrasonic homogenizer for 60 min. The TiO2 suspension was
added to starch solution gradually and mixed for 10 min. Afterward, OA- Tween 80 solution was added to starch solution
gradually and mixed for 10 min.
The starch solution containing TiO2 and OA was homogenized by ultrasonic homogenizer for 7 min. Film forming
solution placed under three UV-C lamps (8w, Phillips, Holland) at a distance of 5 cm. The solutions were stirred
simultaneously with UV irradiation. After 0, 30, 60 and 90 min of UV exposure, the air bubbles were removed and the
solutions were casted into flat, leveled, non-stick disposable 15 cm-Petri dishes. Each of the dishes were contain 43 g
which dried for 48 hours at room temperature. All the film specimens were conditioned at 50-55% relative humidity and
room temperature for 48 hours before subjected to further analysis.
Moisture content (MC), moisture absorption (MA), solubility in water (SW), water vapor permeability (WVP), surface
properties, visual properties and mechanical properties of the film specimens were measured. The chemical structure of
the films was investigated by FTIR spectroscopy. Results and Discussion: The results shown that water contact angle of the starch film was increased by adding OA
and TiO2. But it was decreased after UV exposure of the starch-OA-TiO2 solution. WVP of the starch based films was
decreased by its composition with OA and TiO2. But no change was observed after UV exposure of the starch-OA-TiO2
compositions. MC of the starch-OA-TiO2 film had no change, simultaneously.
However, the tensile strength and Young’s modulus were decreased by adding OA-TiO2. Elongation at break and
tensile energy to break were increased, simultaneously. However, the mechanical properties of the starch-OA-TiO2
nanocomposites were changed by UV exposure but these changes did not follow a specific trend.
Although, whiteness index (WI) and total color difference (ΔE) were not changed by OA-TiO2 composition. But
yellowness index (YI) was changed, simultaneously. After UV irradiation ΔE and YI were increased and WI was
decreased. The results, demonstrated that the virgin starch-OA-TiO2 composition was the best modification method to
decrease the sensibility of starch based films to moisture as a packaging material. UV irradiation at short time (30 min)
was the optimum condition to modify sensibility of the films to moisture and mechanical properties among the UV cured films.
