# Aroma Compound Release from Starches of Different Origins: A Physicochemical Study
## 2 Materials and Methods  
Diacetyl and dl-limonene of 99% purity were obtained from Merck A.G. (Darmstadt, Germany). In Table 1, a comprehensive overview of some of their physicochemical properties is given. Starch granules derived from various botanical sources, including corn, wheat, potato, and rice, were also used in the present research. All these were supplied by Sigma-Aldrich (St. Luis, MO, USA) and have the following product numbers: S9676 for corn (Batch #020N0198), S4251 for potato (Lot#058K01572V), S5127 for wheat (Lot#BCBP4613V), and S7260 for rice (Lot#BCBN7121V). To characterize these starches, several analytical techniques were employed. The specific surface area (SSA) of each starch sample was determined in triplicate using the Micrometrics Tristar 3000 instrument. The N\({}_{2}\) adsorption-desorption isotherms at liquid nitrogen temperature (77 K) were recorded to study the textural properties of the samples using a piece of Micrometrics apparatus (Micromerities Tristar 3000 porosimeter, Norcross, GA, USA). Using the corresponding data, each specific surface area was calculated by the Brunauer, Emmett, and Teller (BET) equation. The calculation of micropores and external surface area was performed by the \(t\)-plot method. An identical amount of each sample was firstly freeze-dried and then placed in a piece of degassing apparatus (Micromerities, FlowPrep 060 sample degas system, Norcross, GA, USA) at 70 \({}^{\circ}\)C under a nitrogen stream for 5 h. Each dried sample was weighed accurately before being placed in the porosimeter. The glass transition temperature (\(T_{\mathrm{g}}\)) of each starch sample was measured using the TG 209 F3 Tarsus instrument from Netzsch (Burlington, MA, USA). Ten (10) mg of each sample was added into the instrument cell and the temperature was regulated from 30 \({}^{\circ}\)C to 300 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **Chemical** & **M\({}_{\mathrm{v}}\)** & **M\({}_{\mathrm{v}}\)** & & & & & & & \\  & **Formula** & **(g mol-1)** & **(cm mol-1)** & **Log P (25 °C)** & **W\({}_{\mathrm{sol}}\) (g L-1) * & \(b_{\mathrm{p}}\) (\({}^{\circ}\)C) \({}^{\mathrm{b}}\)** & **4** & **P\({}_{\mathrm{sat}}\) (mmHg)** & **Odor** & **Descriptor** \\ \hline dl-limonene & C\({}_{\mathrm{pl}}\)H\({}_{\mathrm{id}}\) & 136.24 & 163.3 & 4.57 & 0.0076 & 178 & 0.842 & 1.55 & lemon \\ diacetyl & CaH\({}_{\mathrm{d}}\)O\({}_{\mathrm{2}}\) & 86.09 & 88.8 & \(-\)1.34 & 200.0 & 88 & 0.990 & 56.80 & battery \\ \hline \end{tabular}  
* Data retrieved from the following database: [[https://pubchem.ncbi.nlm.nih.gov/](https://pubchem.ncbi.nlm.nih.gov/)]([https://pubchem.ncbi.nlm.nih.gov/](https://pubchem.ncbi.nlm.nih.gov/)) (accessed on 15 November 2024); \({}^{\mathrm{b}}\) determined at 25 \({}^{\circ}\)C.  
\end{table} 
Table 1: The physicochemical properties of the aroma compounds \({}^{\mathrm{a}}\): molecular weight (\(M_{W}\)), molar volume (\(M_{\mathrm{V}}\)), hydrophobicity (Log \(P\)), water solubility (\(W_{\mathrm{Sol}}\)\({}^{\mathrm{b}}\)), boiling point (\(b_{\mathrm{P}}\), 760 mm Hg), density (\(d\)\({}^{\mathrm{b}}\)), saturated vapor pressure (\(P_{\mathrm{sat}}\)\({}^{\mathrm{b}}\)), and odor descriptor. The morphology and the size distribution of all starches were illustrated by taking photos with a Zeiss Supra 35 VP FEG Scanning Electron Microscope (Carl Zeiss; Oberkochen, Germany). A small amount of each sample was placed on an appropriate holder and covered with a thin layer of conducting material, (Au/Pd) alloy, using a Quorum Q150V Plus Automatic Coater Sputter (East Sussex, UK). Finally, FTIR spectra were obtained for all raw materials used, as well as for the mixtures of different starches and aroma compounds, by using a Cary 630 FTIR Spectrometer (Agilent S.A., Santa Clara, CA, USA) with an ATR sampling module. The collection of FTIR spectra was performed across a wavenumber range of 400 to 4000 cm\({}^{-1}\). The resolution was 2 cm\({}^{-1}\), while the data collection interval was 1 cm\({}^{-1}\).