Commercially Produced Rice and Maize Starches Contain Nonhost Proteins, as Shown by Mass Spectrometry

Abstract

To evaluate the presence of contaminating nonhost proteins in commercially prepared rice and maize starch samples, we initiated a direct sequencing mass spectrometric proteomics survey. We discovered nonhost proteins from a variety of species, including Phytophthora cinnamomi, Homarus americanus, and Ovis aries. Our documentation of H. americanus proteins in these starch samples may have food safety implications with regard to shellfish allergies. We hypothesize that these proteins were introduced to the starch samples via process wash water used in the milling and deproteination steps in the commercial preparation of the starches analyzed. The introduction of nonhost proteins during commercial processing of starch samples that are used routinely in analytical studies indicates that these studies are using impure materials. Therefore, further study and documentation of the starch samples is required to ensure that all components of the samples are properly catalogued.

Three Diverse Granule Preparation Methods for Proteomic Analysis of Mature Rice (Oryza sativa L.) Starch Grain

“…The remaining hydrophobic proteins were released from the starch granule surface by isopropanol solubilization. These protein extraction methods isolated primarily carbohydrate metabolism and seed storage proteins, as expected [ 15 ]. This comprehensive list includes globulins, glutelins, prolamins, and other typical SGAPs such as starch biosynthetic enzymes, starch mobilization enzymes, heat shock proteins (required for normal amyloplast development) [ 35 ], and 14-3-3 proteins (required for the assembly of starch biosynthetic complexes) [ 36 ], as well as putative compound granule framework proteins ( Datasets S1–S6 ).…”

“…The peptides associated with the starch granule surface were collected according to a modified protocol [ 15 , 17 ]. Trypsin-treated granules were centrifuged at 18,000× g for one minute and supernatant was transferred to a fresh tube.…”

“…The missing pieces of information regarding the SG scaffolding or plastoskeleton may be present in the starch granule-associated protein (SGAP) proteome [ 13 , 14 ]. As such, the preparation of SGs and the analysis of the SGAP [ 15 , 16 ] of the rice starch granule is the focus of this study. Mature rice kernels were used in an effort to eliminate any bias that may be introduced by the commercial processing of rice starch [ 15 ].…”

“…As such, the preparation of SGs and the analysis of the SGAP [ 15 , 16 ] of the rice starch granule is the focus of this study. Mature rice kernels were used in an effort to eliminate any bias that may be introduced by the commercial processing of rice starch [ 15 ]. In this study, three methods of starch granule preparation from mature rice kernels (dispersion, microsieve, and flotation) were used, following which phase separation using two different approaches (trypsin shaving and isopropanol solubilization of residual peptides) [ 17 , 18 ] was performed.…”