پديد آورندگان :
بديعي، فوژان سازمان تحقيقات، آموزش و ترويج كشاورزي - موسسه تحقيقات فني و مهندسي كشاورزي، كرج، ايران , مفتون آزاد، ندا سازمان تحقيقات، آموزش و ترويج كشاورزي - مركز تحقيقات و آموزش كشاورزي و منابع طبيعي فارس - بخش تحقيقات فني و مهندسي كشاورزي، شيراز، ايران , معدني، صغري سازمان تحقيقات، آموزش و ترويج كشاورزي - موسسه تحقيقات فني و مهندسي كشاورزي، كرج، ايران , شاه اميريان، مريم سازمان تحقيقات، آموزش و ترويج كشاورزي - مركز تحقيقات و آموزش كشاورزي و منابع طبيعي فارس - بخش تحقيقات فني و مهندسي كشاورزي، شيراز، ايران
كليدواژه :
انجير , پلاستي‌سايزر , دماي انتقال شيشهاي , دماي جابه‌جايي , شاخص قهوه‌اي‌شدگي
چكيده فارسي :
زمينه مطالعاتي: قهوه اي شدگي انجير از جمله تغييرات بيوشيميايي وابسته به دماي انتقال شيشهاي است. هدف: هدف از انجام اين مطالعه بررسي امكان توليد انجير نيمه مرطوب با افزودن پلاستي سايزرها و تاثير آن بر سرعت قهوه اي شدگي و پايداري آن بوده است. روش كار: براي اين منظور انجيرهاي نيمه مرطوب توسط پلاستي سايزرهاي شربت ساكارز، شربت گلوكز و گليسرول در غلظت هاي 25 و 50 درصد آماده و پس از خروج نمونه ها از محلول، در ظروف پلاستيكي غيرقابل نفوذ به هوا بسته بندي شده و در سه سطح دمايي 5، 25 و 35 درجه سانتي گراد نگهداري شدند. خواص حرارتي نمونه ها با استفاده از دستگاه گرماسنج پويشي تفاضلي (DSC) اندازه گيري شد. نتايج: نتايج اندازه گيري دماي انتقال شيشه اي (Tg) نشان داد كه نمونه انجير آبدارشده (شاهد) دماي انتقال شيشه اي كمتري نسبت به ساير نمونه ها دارد. در ادامه پس از سه ماه، ميزان قهوه اي شدگي نمونه ها مطالعه شد. شاخص قهوه اي شدگي انجير در اين مدت در تمام نمونه ها و شاهد به تدريج افزايش يافت. افزايش دماي نگهداري نيز در تمام تيمارها باعث افزايش روند قهوه اي شدگي نمونه ها شد. شاخص قهوه اي شدگي انجير شاهد افزايش معني داري نسبت به ساير نمونه ها نشان داد و رنگ تيره تري نسبت به نمونه هاي تيمارشده با پلاستي سايزرها داشت. در پايان با استفاده از پارامتر دماي جابه جايي (T-Tg) تغييرات شاخص قهوه اي شدگي انجير بررسي شد، صرف نظر از اينكه دماي نگهداري (T) يا پلاستي سايزر (كه روي Tg اثر مي گذارد) تغييركند. نتيجه گيري نهايي: به طور كلي نتايج حاصل از اين پژوهش نشان داد كه شربت گلوكز 50 درصد و شربت ساكارز 50 درصد در كنترل تيرگي و قهوه اي شدگي انجير موثرتر از ساير تيمارها هستند.
چكيده لاتين :
Introduction: Fig (Ficus carica L.) is a very nutritious fruit with high amounts of carbohydrates, minerals and vitamins (Doymaz 2005). This fruit is highly perishable with a very short storage life even in refrigerator. Therefore, it is mostly used in dried form (Farahnaky et al., 2009). Although drying is a suitable way to improve its shelf-life, producing semi-dried fig leads to improving the marketability of this fruit. However, due to higher water activity, semi-dried figs with intermediate moisture content have short storage life and undergo physical, chemical and sensorial changes. Browning is the major problem that takes place in dried and semi-dried fruits during storage and has a great negative impact on their consumption and marketability. The browning of food products results from enzymatic and non-enzymatic reactions. Polyphenol oxidase is the major enzyme responsible for enzymatic browning in fruits (Giang et al., 2016). However, non‐enzymatic browning is often associated with maillard reaction and ascorbic acid degradation (Yamada et al., 2009). Controlling water activity plays an important role in reducing non-enzymatic browning. Plasticizers like mono-, di- and oligosaccharides (glucose and sucrose syrup and honey), polyols (glycerol, sorbitol and glycerol derivatives) and fats and their derivatives can reduce water activity and change the glass transition temperature. The objective of this study was to produce semi-dried figs using different plasticizers and to investigate the effects of plasticizers on browning kinetics and stability of fig with intermediate moisture content.
Material and methods: Semi-dried figs (cv. Sabz) were obtained by adding different plasticizers of sucrose syrup at concentrations of 25, 50 (W/V), glucose syrup at concentrations of 25 and 50 % (W/V) and glycerol at two concentrations of 25 and 50 % (V/V). The rehydrated figs were considered as control. All the samples were kept in airtight containers at three temperatures of 5, 25 and 35oC. Thermal properties of the samples were measured using differential scanning calorimetry (DSC). Browning index was obtained by measuring three color dimensions of L* (lightness or brightness), a* (redness or greenness) and b* (yellowness or blueness) values of the plasticized figs and control. Microscopic structures of different fig samples were observed by scanning electron microscopy. A completely randomized design was used to assess the effect of adding different plasticizers and storage temperature on the browning index of figs independently. All the experiments were carried out in three replications. Analysis of the results (ANOVA one-way) was done using SPSS statistical software version 19 at probability value of 5% (p < 0.05) and the mean significant difference was assessed using Duncan's multiple range tests.
Results and discussions: DSC thermograms of fig samples showed a stepwise change associated to the glass transition of amorphous regions. By adding different plasticizers, the moisture content of semi-dried figs decreased and their Tg shifted to higher temperatures compared to the control. The results showed that the glass transion temperature (Tg) of the rehydrated fig (control) was lower than that of other plasticized figs, which shows that water is the most effective plasticizer for food systems. Then, browning index of the figs was measured after 3 months. Browning index rose significantly during storage time. Furthermore, by increasing storage temperature, the values of browning index increased significantly and it was higher for the control compared to the other plasticized samples. This means that control figs were darker than the plasticized samples over the whole storage time. Finally, the concept of shifted temperature parameter (T-Tg) was used to account for the effects of storage temperature (T) and plasticizers (through Tg) on the changes of fig browning index. Microscopic images of fig samples showed that rehydrated fig had a porous structure. By increasing the concentration of glucose syrup to 50%, the structure of fig became less porous and as a result of saturation, glucose crystal was appeared on the surface. The same structure was observed for the plasticized figs with sucrose syrup. Plasticized figs with glycerol had denser and non-porous structure.
Conclusion: Fig browning is a biochemical change which is dependent on glass transition. The rate of browning was expressed by the shifted temperature parameter (T-Tg) and increased by increasing shifted temperature, regardless of whether T or Tg was varied. The overall results showed that 50 % glucose syrup and 50 % sucrose syrup are the most effective treatments to control the browning of fig fruit.
