Thermal transitions of gelatin evaluated using DSC sample pans of various seal integrities
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Thermal transitions of gelatin evaluated using DSC sample pans of various seal integrities Indraneil Mukherjee • MaryAnn Rosolen
Received: 21 February 2013 / Accepted: 28 March 2013 Ó Akade´miai Kiado´, Budapest, Hungary 2013
Abstract Differential scanning calorimetry (DSC) has become a popular tool to investigate thermal transitions in food ingredients such as gelatin. Upon heating commercial gelatin samples beyond glass transition (Tg) and melting (Tm) temperatures, a relatively large endothermic transition (Ti) can be observed. We have observed that both the peak temperature and the enthalpy of the Ti transition are influenced by the integrity of the seal of the DSC pans used for the analysis. This study shows that escape of moisture from the DSC pan appears to be responsible for this effect. The effect of different types of DSC pans, as well as technique of sealing them on the Ti transition were evaluated using DSC, SDT, and TG–MS. Keywords Gelatin Temperature of isomerization DSC pan Seal integrity TG–mass spectrometry (TG–MS) Simultaneous DSC–TG (SDT)
Introduction Gelatin is a non-homogeneous but chemically well defined, translucent, odorless, nearly tasteless solid material obtained upon extraction and hydrolysis of the collagen from animal bones, connective tissues or skin [1]. Aqueous solutions of gelatin are in the sol state at 40 °C and form thermo-reversible gels upon cooling due to the recovery of collagen triple helices via a conformational disorder–order transition of the chains [2]. This behavior lends unique organoleptic properties to gelatin which has led to its use as I. Mukherjee (&) M. Rosolen Kraft Foods Global, Inc., 555 S. Broadway, Tarrytown, NY 10591, USA e-mail: [email protected]
a gelling, thickening, and stabilizing agent in foods [3]. Being a fibrous protein, gelatin is effectively plasticized by water and alcohols, which results in lowering of glass transition temperature (Tg) and unfolding (Tm) [4, 5]. This has serious impact on the processing, storage, and texture of gelatin-containing foods such as ice creams, marshmallows, Jell-OTM, etc. Understanding the thermal properties of gelatin is therefore vital to food technologists. Differential scanning calorimetry (DSC) has been used as a prominent tool to investigate the thermal properties of gelatin in various forms [4–12]. DSC involves subjecting a sample and a reference pan to the same temperature profile and measuring heat flow. It is a technique, which can accurately determine the temperatures and enthalpies associated with phase transitions and has therefore found widespread application in the food industry [13]. The technique relies on the sample and reference pans being identical, both in construction and in contact with the heat source [14]. For relatively high moisture materials, such as food systems or liquids, results can be affected by the escape of volatiles from the DSC pan [15, 16]. As known in the literature, a DSC heating scan of commercial gelatin (containing *10 mass% moisture) reveals a sec
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