Marisa M. Wall's research while affiliated with Hawaii Agriculture Research Center and other places

Taro (Colocasia esculenta) flour is a viable carbohydrate alternative and a functional additive for food formulation; however, different taro varieties may possess distinct characteristics that may influence their suitability for food production. This study evaluated the nutritional, physicochemical, and functional properties of flours from five Hawaiian taro varieties: Bun‐Long, Mana Ulu, Moi, Kauaʻi Lehua, and Tahitian. Tahitian, Bun‐long, and Moi had high total starch contents of 40.8, 38.9, and 34.1 g/100 g, respectively. Additionally, Moi had the highest neutral detergent fiber (25.5 g/100 g), lignin (1.39 g/100 g), and cellulose (5.31 g/100 g). In terms of physicochemical properties, Tahitian showed the highest water solubility index (33.3 g/100 g), while Tahitian and Moi exhibited the two highest water absorption indices (5.81 g/g and 5.68 g/g, respectively). Regarding functional properties, Tahitian had the highest water absorption capacity (3.48 g/g), and Tahitian and Moi had the two highest oil absorption capacities (3.15 g/g and 2.68 g/g, respectively). Therefore, the flours from these Hawaiian taro varieties possess promising characteristics that could enhance food quality when used as alternative additives in food processing.

An electrochemical immunosensor has been developed for the rapid detection and identification of potentially harmful bacteria in food and environmental samples. This study aimed to fabricate a microwire-based electrochemical immunosensor (MEI sensor) for selective detection of Escherichia coli and Staphylococcus aureus in microbial cocktail samples using dielectrophoresis (DEP)-based cell concentration. A gold-coated tungsten microwire was functionalized by coating polyethylenimine, single-walled carbon nanotube (SWCNT) suspension, streptavidin, biotinylated antibodies, and then bovine serum albumin (BSA) solutions. Double-layered SWCNTs and 5% BSA solution were found to be optimized for enhanced signal enhancement and nonspecific binding barrier. The selective capture of E. coli K12 or S. aureus cells was achieved when the electric field in the bacterial sample solution was generated at a frequency of 3 MHz and 20 Vpp. A linear trend of the change in the electron transfer resistance was observed as E. coli concentrations increased from 5.32 × 102 to 1.30 × 108 CFU/mL (R2 = 0.976). The S. aureus MEI sensor fabricated with the anti-S. aureus antibodies also showed an increase in resistance with concentrations of S. aureus (8.90 × 102–3.45 × 107 CFU/mL) with a correlation of R2 = 0.983. Salmonella typhimurium and Listeria monocytogenes were used to evaluate the specificity of the MEI sensors. The functionalization process developed for the MEI sensor is expected to contribute to the sensitive and selective detection of other harmful microorganisms in food and environmental industries.

High-throughput sequencing was used to analyze Hibiscus rosa-sinensis (family Malvaceae) plants with virus-like symptoms in Hawaii. Bioinformatic and phylogenetic analysis revealed the presence of two tobamoviruses, hibiscus latent Fort Pierce virus (HLFPV) and a new tobamovirus with the proposed name "hibiscus latent Hawaii virus" (HLHV). This is the first report of the complete sequence, genome organization, and phylogenetic characterization of a tobamovirus infecting hibiscus in Hawaii. RT-PCR with virus-specific primers and Sanger sequencing further confirmed the presence of these viruses. Inoculation experiments showed that HLFPV could be mechanically transmitted to Nicotiana benthamiana and N. tabacum, while HLHV could only be mechanically transmitted to N. benthamiana.

Hibiscus (Hibiscus spp., family Malvaceae) leaves exhibiting symptoms of mosaic, ringspot, and chlorotic spots were collected in 2020 on Oahu, HI. High-throughput sequencing analysis was conducted on ribosomal RNA-depleted composite RNA samples extracted from symptomatic leaves. About 77 million paired-end reads and 161,970 contigs were generated after quality control, trimming, and de novo assembly. Contig annotation with BLASTX/BLASTN searches revealed a sequence (contig 1) resembling the RNA virus, hibiscus chlorotic ringspot virus (genus Betacarmovirus), and one (contig 2) resembling the DNA virus, peanut chlorotic streak virus (genus Soymovirus). Further bioinformatic analyses of the complete viral genome sequences indicated that these viruses, with proposed names of hibiscus betacarmovirus and hibiscus soymovirus, putatively represent new species in the genera Betacarmovirus and Soymovirus, respectively. RT-PCR using specific primers, designed based on the retrieved contigs, coupled with Sanger sequencing, further confirmed the presence of these viruses. An additional 54 hibiscus leaf samples from other locations on Oahu were examined to determine the incidence and distribution of these viruses.

Pineapple (Ananas comosus L. [Merr.]) accessions from the U.S. Tropical Plant Genetic Resources and Disease Research (TPGRDR) in Hilo, Hawaii were subjected to RNA-sequencing to study the occurrence of viral populations associated with this vegetatively propagated crop. Analysis of high-throughput sequencing data obtained from 24 germplasm accessions and public domain transcriptome shotgun assembly (TSA) data identified two novel sadwaviruses, putatively named “pineapple secovirus C” (PSV-C) and “pineapple secovirus D” (PSV-D). They shared low amino acid sequence identity (from 34.8 to 41.3%) compared with their homologs in the Pro-pol region of the previously reported PSV-A and PSV-B. The complete genome (7485 bp) corresponding to a previously reported partial sequence of the badnavirus, pineapple bacilliform ER virus (PBERV), was retrieved from one of the datasets. Overall, we discovered a total of 69 viral sequences representing ten members within the Ampelovirus, Sadwavirus, and Badnavirus genera. Genetic diversity and recombination events were found in members of the pineapple mealybug wilt-associated virus (PMWaV) complex as well as PSVs. PMWaV-1, -3, and -6 presented recombination events across the quintuple gene block, while no recombination events were found for PMWaV-2. High recombination frequency of the RNA1 and RNA2 molecules from PSV-A and PSV-B were congruent with the diversity found by phylogenetic analyses. Here, we also report the development and improvement of RT-PCR diagnostic protocols for the specific identification and detection of viruses infecting pineapple based on the diverse viral populations characterized in this study. Given the high occurrence of recombination events, diversity, and discovery of viruses found in Ananas germplasm, the reported and validated RT-PCR assays represent an important advance for surveillance of viral infections of pineapple.

The microbiological safety of avocado is concerning in light of associated foodborne illness outbreaks. Avocados were inoculated with 7 log CFU/fruit of Salmonella enterica serovar Typhimurium or Listeria monocytogenes and stored at 21 °C for 10 days and 7 °C for 14 days. S. Typhimurium level increased by 0.71 log CFU/fruit at 21 °C and decreased by 0.93 log CFU at 7 °C (P < 0.05). L. monocytogenes remained stable at 6.95–7.27 log CFU/fruit at both temperatures. In the sanitation experiment, avocados were inoculated with 8 log CFU/fruit of the bacteria and treated with chlorine dioxide (ClO2) produced with HCl or malic acid (10, 15, 20 ppm) and peroxyacetic acid (PAA; 60, 80, 100 ppm) for 5 min. Fifteen and twenty ppm malic-acid-produced ClO2 and 100 ppm PAA reduced S. Typhimurium to an undetectable level. Twenty ppm ClO2 produced with malic acid showed the highest L. monocytogenes reduction of 6.93 log CFU. This study revealed the potential survival and growth of pathogenic bacteria on fresh avocado stored under household conditions. ClO2 or PAA showed potential to serve as alternative sanitizers in avocado washing, although further confirmation in the industrial settings and the evaluation of their impact on avocado sensory properties are warranted.

The complete genome sequence of pineapple secovirus B (PSV-B), a new virus infecting pineapple ( Ananas comosus ) on the island of Oahu, Hawaii, was determined by high-throughput sequencing (HTS). The genome comprises two RNAs that are 5,956 and 3,808 nt long, excluding the 3’-end poly-A tails, both coding for a single large polyprotein. The RNA1 polyprotein contains five conserved domains associated with replication, while the RNA2 polyprotein is cleaved into the movement protein and coat protein. PSV-B is representative of a new species in the subgenus Cholivirus (genus Sadwavirus ; family Secoviridae ), as the level of amino acid sequence identity to recognized members of this subgenus in the Pro-Pol and coat protein regions is below currently valid species demarcation thresholds.

Taro (Colocasia esculenta), a starchy root crop, is widely consumed across Asia and the Pacific and exists as different colored varieties in Hawai‘i. Although nutritional information exists for taro, there is a lack of variety-specific compositional data. In this study, the nutrient content (proximate and mineral via ICP-OES), phytochemical content (carotenoid via HPLC-PDA, total phenolic via Folin-Ciocalteau assay, and total monomeric anthocyanin via pH differential method), and carotenoid bioaccessibility (digestibility and micellarization efficiency via three-stage simulated digestion) were compared for three non-commercial taro, Mana Ulu, Pi‘iali‘i, and immature Pi‘iali‘i (Keiki) with one commercial variety, Maui Lehua. Nutrient and phytochemical contents differed across each taro cultivar based on their raw and cooked forms (P< 0.05). Beta-carotene and lutein were the primary carotenoids across each cultivar, with Mana Ulu containing the highest carotenoid concentration. Beta-carotene exhibited digestive stability of 45.8% and a micellarization efficiency of 13.6% from Mana Ulu samples. Total phenolic content was 83.52, 76.04, 75.44, and 66.86 mg/100 g FW and total anthocyanin content of 10.02, 9.33, 7.32, and 6.93 mg/100g FW for Maui Lehua, Mana Ulu, Pi‘iali‘i Keiki, and Pi‘iali‘i, respectively. Cooked taro had significant polyphenol losses with total phenolic contents of 20.55, 17.73, 22.61, 25.93 mg/100g FW, as well as total anthocyanin contents of 3.19, 2.16, 2.12, and 2.88 mg/100g FW for Maui Lehua, Mana Ulu, Pi‘iali‘i Keiki, and Pi‘iali‘i, respectively. These findings indicate unique nutritional and phytochemical profiles amongst underutilized taro varieties, which could be better leveraged to improve nutrition and health outcomes. Overall, expanding variety-specific compositional data is critical to ensure reliable database information to assess the nutritional adequacy of diets.