Changing the Landscape: An Introduction to the Agricultural and Food Chemistry Technical Program at the 258th American Chemical Society National Meeting in San Diego

This special issue of the Journal of Agricultural and Food Chemistry (JAFC) is a highlight of the Agricultural and Food Chemistry Division (AGFD) technical program at the 258th National Meeting of the American Chemical Society (ACS) in San Diego, CA, U.S.A., on August 25-29, 2019. At the conference, AGFD had 44 oral sessions at 19 symposia and 100 poster presentations with more than 400 abstract submissions. The technical program covered a broad range of current research and development topics in agricultural and food chemistry, including bioactive food components, diet and human nutrition, utilization of agricultural materials in food systems, food packaging, nanotechnology, and food safety, as well as several special award symposia. This is the first JAFC special issue that highlights an ACS national meeting program with joint efforts from AGFD.

Cellulose nanocrystal driven microphase separated nanocomposites: Enhanced mechanical performance and nanostructured morphology

The interest in the modification of cellulose nanocrystals (CNCs) lies in the potential to homogenously disperse CNCs in hydrophobic polymer matrices and to promote interfacial adhesion. In this work, poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) (PBA) were grafted onto CNCs, thereby imparting their hydrophobic traits. The successful grafting modification led to the increased thermal stability of modified CNCs (MCNCs), and the hydrophobic surface modification was integrated with crystalline structure and morphology of CNCs. The nanocomposites with 7 wt% MCNCs/PBA-co-PMMA had an increase in Young's modulus of >25-fold and in tensile strength at about 3 times compared to these of neat PBA-co-PMMA copolymer. In addition, a micro-phase separated morphology (PBA soft domains, and PMMA and CNC hard domains) of MCNCs/PBA-co-PMMA nanocomposites was observed. The large increase in the storage moduli (glass transition temperatures) and organized morphology of MCNCs/PBA-co-PMMA nanocomposites also elucidated the relationship between mechanical properties and micro-phase separated morphology. Therefore, the MCNCs are effective reinforcing agents for the PBA-co-PMMA thermoplastic elastomers, opening up opportunities for their wide-spread applications in polymer composites.

NMR Analysis of Poly(Lactic Acid) via Statistical Models

The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. In this work, we prepared several PLA samples with a tin catalyst at different L,L-lactide and D,D-lactide ratios. Upon analysis of the tetrad intensities with the pair-addition Bernoullian model, we found substantial deviations between observed and calculated intensities due to the presence of transesterification and racemization during the polymerization processes. We formulated a two-state (pair-addition Bernoullian and single-addition Bernoullian) model, and it gave a better fit to the observed data. The use of the two-state model provides a quantitative measure of the extent of transesterification and racemization, and potentially yields useful information on the polymerization mechanism.

Preparation and Characterization of Carboxymethyl Cellulose Films with Embedded Essential Oils

There is current interest in using biobased materials to produce food packaging that can increase the shelf-lives of fruits and vegetables and minimize food spoilage in supermarkets and at the same time not generating plastic waste that causes long-term disposal problems. A good candidate for such materials is the polysaccharide, such as carboxymethyl cellulose (CMC), which is edible and biodegradable. In this work films were produced from two CMC materials with different degrees of substitution (DS) that encapsulated four different essential oils (eugenol, rosemary oil, coriander oil, and nutmeg oil) that are known to have beneficial properties for food applications. The mechanical properties, opacity, and water vapor permeation were evaluated. In general, the essential oil-embedded CMC with the two DS values behaved rather differently. In particular, the essential oil-embedded CMC with 0.7 DS degree of substitution gave stronger and more flexible films and may be more suited for use in food packaging.

NMR analysis of compositional heterogeneity in polysaccharides

Many copolysaccharides are compositionally heterogeneous, and the composition determined by the usual analytical or spectroscopic methods provides only an average value. For some polysaccharides, the NMR data contain copolymer sequence information, such as diad, triad, and tetrad sequence intensities. In such cases, it is possible to estimate the extent of compositional heterogeneity through NMR. Two general types of methodologies can be used: perturbed Markovian and discrete component approaches. The theoretical bases for these approaches are reviewed in this work, and three examples are shown of the application of these NMR methodologies to copolysaccharides.

Comparison of the Adhesive Performances of Soy Meal, Water Washed Meal Fractions, and Protein Isolates

Adhesive bonding of wood plays an increasing role in the forest products industry and is a key factor for efficiently utilizing timber and other lignocellulosic resources. In this work, we obtained five soy meal products through commercial sources or in-house preparations. The protein content was 49.6%, 56.9%, 66.2%, 86.3%, and 91.9% for untreated defatted soy meal, pH 8.5 water washed meal, neutral water washed meal, commercial protein isolate, and in-house prepared protein isolate. The adhesive performances measured by the maximal dry and soaked shear strength of the bonded maple veneers at break were not exactly in the same order of the protein content, indicating that other components (e.g. carbohydrates, metals) might also have played certain roles in the adhesive ability of these products. Data at two press temperatures (i. e. 100, and 130 ^oC) with or without the addition of tung oil revealed that water washed soy meals behaved more like untreated meal than soy protein isolates. This observation is different from a recent report on the effect of water washing on cottonseed meal products. Thus, further elucidation of the mechanisms or causes of the differing effects of water washing would shed light on the adhesive mechanisms of the two types of oilseed meal materials, thus optimizing use of these materials and their fractions for wood bonding.

129Xe NMR studies of morphology and accessibility in porous biochar from almond shells

¹²⁹Xe NMR EXSY plot demonstrating pore connectivity in sustainable almond shell biochar generated from anaerobic thermal activation and rainwater washing.

Preparation of acetonides from soybean oil, methyl soyate, and fatty esters

This paper describes the preparation of a new type of branched vegetable oil and its methyl ester that involves the formation of acetonides. A facile and environmentally friendly synthesis has been found to produce acetonides that entails the use of ferric chloride as a catalyst and is conducted at room temperature. The products have been fully characterized with the help of model compounds, including elemental analysis, infrared (IR) spectroscopy, nuclear magnetic resonance (NMR), and gas chromatography-mass spectrometry (GC-MS).

Synthesis of an amine-oleate derivative using an ionic liquid catalyst

A facile (and environmentally friendly) reaction between epoxidized methyl oleate and aniline to produce an oleate-aniline adduct, without the formation of fatty amide, was discovered. This reaction was carried out neat, with a catalytic amount of an ionic liquid. No solvent was used, no byproducts were produced, and the ionic liquid could be recovered and recycled. The reaction products were fully characterized by NMR and GC-MS.

Azide derivatives of soybean oil and fatty esters

An environmentally friendly water-based pathway to form the azide derivatives of soybean oil and fatty esters is reported. This entails first the formation of epoxides and then the azidization of the epoxides. The azidization reaction is carried out at high yields in water with only a small amount of an ionic liquid as a catalyst. The distribution of azide and alcohol functionalities on the fatty acid moiety is approximately random. This reaction has been applied to methyl oleate, methyl linoleate, soybean oil, and methyl soyate. The resulting structures have been studied by NMR.