Relative importance of moisture migration and amylopectin retrogradation for pound cake crumb firming.

Moisture migration largely impacts cake crumb firmness during storage at ambient temperature. To study the importance of phenomena other than crumb to crust moisture migration and to exclude moisture and temperature gradients during baking, crustless cakes were baked using an electrical resistance oven (ERO). Cake crumb firming was evaluated by texture analysis. First, ERO cakes with properties similar to those baked conventionally were produced. Cake batter moisture content (MC) was adjusted to ensure complete starch gelatinisation in the baking process. In cakes baked conventionally, most of the increase in crumb firmness during storage was caused by moisture migration. Proton nuclear magnetic resonance ((1)H NMR) showed that the population containing protons of crystalline starch grew during cake storage. These and differential scanning calorimetry (DSC) data pointed to only limited amylopectin retrogradation. The limited increase in amylopectin retrogradation during cake storage cannot solely account for the significant firming of ERO cakes and, hence, other phenomena are involved in cake firming.

Low resolution 1H NMR assignment of proton populations in pound cake and its polymeric ingredients.

Based on a model system approach, five different proton populations were distinguished in pound cake crumb using one dimensional low resolution (1)H NMR spectroscopy. In free induction decay (FID) measurements, proton populations were assigned to (i) non-exchanging CH protons of crystalline starch, proteins and crystalline fat and (ii) non-exchanging CH protons of amorphous starch and gluten, which are in little contact with water. In Carr-Purcell-Meiboom-Gill (CPMG) measurements, three proton populations were distinguished. The CPMG population with the lowest mobility and the FID population with the highest mobility represent the same proton population. The two CPMG proton populations with the highest mobility were assigned to exchanging protons (i.e., protons of water, starch, gluten, egg proteins and sugar) and protons of lipids (i.e., protons of egg yolk lipids and amorphous lipid fraction of margarine) respectively. Based on their spin-lattice relaxation times (T1), two dimensional (1)H NMR spectroscopy further resolved the two proton populations with the highest mobility into three and two proton populations, respectively.