Progress report for GNE21-273
The main objective is to rebrand and increase the marketability and utilization of squashes grown in NJ by developing squash-noodle-based value-added low-carb healthy meal solutions, packed in 100% recyclable trays with functional and convenient microperforated peel-reseal lidding films. To achieve this objective, our project will overcome the challenges in processing and packaging squash noodles. Listed below are the sub-objectives.
- We will address microbial safety in the processing of squash noodles, including both butternut squash and zucchini. From 2019 to January 2021, 5 recalls have been issued on fresh-cut squashes and squash noodles in the U.S., all due to Listeria monocytogenes contamination. FDA-approved sanitizers, such as chlorine-based sanitizer and peroxyacetic acid (PAA), are the readily available and economically feasible options to wash squashes in squash noodles processing. Therefore, we will optimize the type of wash-water sanitizer, washing time, washing method, and other parameters in squash noodles processing to improve microbial safety.
- We will optimize the performance of peel-reseal lidding films. What limited the application of peel-reseal films in fresh produce packaging is the whitening of pressure-sensitive adhesive (PSA) and the loss of adhesion, due to PSA’s contact with the respiratory condensates from fresh produce. Therefore, we will screen suitable PSAs, develop methods to prevent PSA whitening, and optimize the adhesion strength to develop peel-reseal films for squash noodles packaging.
- We will design Modified Atmosphere Packaging (MAP) with microperforated peel-reseal films to retain the quality of squash noodles and extend the shelf-life. Compared to squashes cut into cubes or chips, squash noodles have more surface area exposed to air and more plant tissues damaged during processing, resulting in faster respiration rates, senescence, and shorter shelf-life. Therefore, we will design films with oxygen transmission rate (OTR) specific to butternut squash and zucchini noodles to maintain the optimum gas levels in the package, and we will evaluate the effect of MAP on quality retention of squash noodles.
The purpose of this project is to increase the marketability and utilization of squashes grown in New Jersey (NJ) by developing a 100% squash-based value-added low-carb healthy meal solution, packed in 100% recyclable trays with functional and convenient peel-reseal lidding films. The peel-reseal lidding film is microperforated to modify the atmosphere inside the tray to help protect quality and extend shelf-life. We envision our product to be nutritious, healthy, and able to provide additional functions including branding, convenience, freshness, and visibility, which would help NJ farmers rebrand squashes and utilize them to their full potentials.
New Jersey squash production and sales
Squash is an important crop in New Jersey, grown on 3,800 acres with a value of $11,056,000 in 2020. However, the utilization of squashes in NJ has been declining since 2016, as shown in Fig. 1. As a result, squash farmers in NJ are experiencing significant but still growing economic losses from squashes that are harvested but unsold, as shown in Fig. 2, from theoretically 0 in 2016, since all squashes were utilized, to around 2 million dollars in 2019-2020. In 2020 alone, 4,560,000 pounds of squashes (equals to $2,106,720), accounting for 16% of total squash produced, were unsold. The economic losses are impairing the sustainability of squash farming in NJ and impacting even wider agricultural communities.
Our solution for sustainable agriculture
Our solution is to add value to local squashes by developing healthy meal solutions based on squash noodles—squashes cut into the shape of spiral noodles—and packing the product in 100% recyclable trays with microperforated peel-reseal lidding films.
The value of squashes is multiplied when the squashes are produced into noodles. Noodles made from butternut squashes and zucchinis are considered as low-carb alternatives for pasta or noodles, as they contain only about 1/3–1/10 of the carbohydrates and Calories in pasta, as shown in Fig. 3. Moreover, squash is gluten-free, and rich in nutrients such as potassium, zinc, vitamin C, dietary fiber, and antioxidants such as zeaxanthin, lutein, and beta-carotene. Therefore, squash noodles offer great value for customers, especially the expanding single households and millennial groups, who are constantly looking for healthier meal solutions that are half-ready, convenient, but somehow still require their cooking. By packing the product in 100% recyclable trays with microperforated peel-reseal lidding films, we can add more value to squash noodles, as it brings customers convenience, freshness, quality, shelf-life extension, and ties in customers’ growing environmental awareness. With all the added value, NJ farmers can rebrand and increase the marketability of local squashes, reduce their economic losses from unsold squashes, and achieve a more sustainable agriculture.
Figs. 1, 2. Utilization and unsold value of squashes in New Jersey. Data were calculated from the estimated numbers provided by nj.gov.
Fig. 3. Comparison between the nutrition value of 100 grams of zucchini noodles, butternut squash noodles, and spaghetti
Addressing microbial safety in squash noodles processing
To investigate the effect of different processing parameters on the microbial safety of squash noodles, experiments will be performed based on a two-level factorial design. Table 1 lists the 5 factors identified and the assigned low/high levels. The high level of sanitizer concentration will be 200 ppm and 80 ppm for chlorinated water and PAA, respectively, according to the maximum suggested concentration from legislation and literature [10, 11]. Outputs from experiments will be the log reduction of L. monocytogenes and Escherichia coli O157:H7 on squash surfaces (CFU/cm2). Based on the design of experiment, each run will contain 32 tests, and runs will be performed in triplicate. With the collected data, regression analysis will be performed to analyze how the use of sanitizer, type of sanitizer, type of produce, treatment method, and treatment time can affect the growth of pathogens on squash surfaces.
Table 1. Factors and associated levels in the design of experiment
All the experiments will be performed in a biosafety level 2 microbiology laboratory. Butternut squash (Cucurbita moschata) and zucchini (C. pepo var. cylindrica) will be purchased from local farms and cut into 5 cm (length) 5 cm (width) 1 cm (thickness) pieces. 1 ml of selected strains of L. monocytogenes and E. coli O157:H7 from tryptic soy broth (TSB) with an initial concentration of 106-7 CFU/mL will be inoculated on surfaces of the pre-cut squash skins, and then air-dried for 1 h. The inoculated squash skins will be then treated according to the design of experiment. Chlorinated water will be made by dissolving sodium hypochlorite in water, and sodium bisulfate will be used to maintain the solution pH at 7. PAA solution will be made by diluting commercially available PAA sanitizer, and acetic acid will be used to maintain the solution pH at 7. Due to the degradation of PAA, its concentration will be monitored hourly using iodometric titration, and more solution will be supplemented as needed. Soaking treatment will be performed by submerging the inoculated surface of squash skins in the solution, and the solution will be replaced periodically to avoid cross-contamination. Spraying treatment will be performed by vertically spraying the solution to the inoculated surface using sterilized sprayers. Survived pathogens from sanitizer treatment will be quantified by juicing the treated squash skins with 20 mL TSB using blenders and counting on tryptic soy agar (TSA) after incubation, while inoculated but untreated squash skins will be used as control groups; excessive fleshes will be removed before juicing, and dilution will be carried out when necessary.
Optimization of PSA formulation, coat weight, and adhesion strength
In peel-reseal films, Pressure Sensitive Adhesive (PSA) provides the resealable feature. To optimize the performance of peel-reseal films, we need to optimize the PSA formulation to achieve acceptable viscosity, good resistance against the whitening from respiratory condensate of fresh produce, and optimal adhesion strength. Twenty PSAs from different suppliers will be screened. These PSAs can be categorized into either acrylic emulsion or rubber-based emulsion, and all the selected PSAs are water-borne, approved for direct and/or indirect food contact, and have been used for labels in food packaging. Their resistance against whitening will be evaluated after stored in airtight chambers at 0 and 90-95% RH for 24 h while coated on 5’’5’’ PET films, based on the following rating scale: 1) heavy whitening, 2) moderate whitening, 3) minimum whitening, and 4) no whitening. The coating of PSA emulsion will be performed using an automatic coater (Sheen Instrument, Metamora, MI), with spiral rods at size 18 moving at the speed of 2.5 mm/s.
Coat weight and adhesion strength optimization will be done using PSA emulsions with high whitening resistance ratings. Four different coat weights — 3, 5, 10, and 20 g/m2 will be tested to investigate the minimum coat weight that provides the target adhesion strengths, which are initial adhesion strength at 150-500 g/in and subsequent adhesion strength at 50-70 g/in after peeling and resealing. Coatings will be performed on 10’’ 10’’ untreated PET films using an automatic coater (Sheen Instrument, Metamora, MI) with spiral rods at sizes 3, 6, and 12 to achieve the target coat weights, respectively, while moving at a speed of 2.5 mm/s. The coated films will be oven-dried at 180 until there is no further change in weight. When the coated films are still warm, they will be then adhered onto another 10’’ 10’’ diet-cut heat-sealable PET film, while ensuring no air is trapped between different layers. Adhesion strengths between the PSA layer and the heat-sealable layer will be measured following ASTM F904-16 for 15-20 peel-reseal cycles.
OTR specific to squash noodles, MAP, and shelf-life evaluation
The OTR specific to squash noodles will be calculated using Equation 1, where RRO2 is the respiration rate of the product (volume per unit weight of squash noodles per unit time), W is product weight, A is film surface area, Patm is atmospheric pressure, O2 air is atmospheric oxygen concentration, and O2 pkg is the desired oxygen concentration in the package. Among these parameters, O2 pkg will be set at 1% and 5% for zucchini noodles and butternut squash noodles, respectively, according to the recommendation from Gorny, and RRO2 will be measured by the following unsteady-state method. 50 g of sanitized zucchini or butternut squash noodles, with a diameter of 3 mm, will be stored in hermetic impermeable chambers with oxygen concentration at 1% (zucchini) or 5% (butternut squash), at 5°C(mimicking optimal storage temperature), 10°C, and 25°C(mimicking temperature abuse), while the change of oxygen concentrations in the chamber will be monitored hourly for 72 hours by an O2/CO2 analyzer (Oxybaby, Witt, Germany); RRO2 will be calculated by plotting oxygen concentration in the chamber against time, and curve-fitting with non-linear regression using Equation 2, where Coxygen is oxygen concentration, t is time, and C0, a, and b are coefficients. The volume of squash noodles will be pre-measured to calculate the headspace volumes in chambers. The result from the calculation will be a range of OTR that squash noodles require at a range of temperature they may undergo during distribution, storage, and consumption.
The OTR specific to squash noodles will be then compared with the achievable OTR of the optimized peel-reseal films and microperforations to determine the size and quantity of microperforations. Achievable package OTRs can be calculated by Equation 3, where Afilm is the surface area of lidding film, and Atotal is the total surface area of the package. The equation is developed using 100% recyclable PET trays as the bottom trays; therefore, the OTR of bottom trays is excluded from the calculation as it is negligible, but if other permeable trays are used, such as bio-based biodegradable fiber trays, the OTR of bottom trays will be included. To investigate whether the peel-reseal films can support the respiration of squash noodles at various temperatures to maintain the optimum oxygen concentration, the temperature dependence of OTR will be calculated using the Arrhenius equation (Equation 4) based on zero-order reaction, where A is constant, Ea is the activation energy, R is the ideal gas law constant, and T is the absolute temperature. OTR of peel-reseal films at various temperatures will be measured by permeation cells designed based on ASTM F2622.
To evaluate the performance of the proposed peel-reseal films with product-specific OTR, the shelf-life of squash noodles packed in packaging with peel-reseal films will be evaluated, while using squash noodles packed in packaging with conventional rigid lids as the control group. Zucchini and butternut squash noodles at three different thicknesses, with diameters of 2 mm, 3 mm, and 5 mm will be produced by table-top spiralizer (Sboly, Guangdong, China) to mimic capellini, spaghetti, and fettuccine, respectively. The squash noodles at different thicknesses will react differently to the modified atmosphere due to their different sensitivities to oxygen, as the result of their different surface areas per unit weight. Squash noodles with a diameter of 2 mm will be more sensitive to oxygen because they have a larger surface area, and more plant tissues are damaged during processing. To pack the squash noodles, 5 to 7 oz sanitized squash noodles will be filled in the PET trays (Cool Pak, Oxnard, CA). The peel-reseal film will be heat-sealed on trays using a table-top tray sealing machine (ER-900, ER Technical Group), and rigid lids that are compatible with the PET trays will be hermetically locked in place. The packed products will be stored at 5°C , 10°C , and 25°C . At least 10 replicas will be created for each group of zucchini and butternut squash noodles at different thicknesses packed in different packages to provide enough samples for shelf-life studies. The shelf-life of squash noodles packed in different packages at different temperatures will be evaluated by the daily measurement of headspace oxygen and CO2 using O2/CO2 analyzer (Oxybaby, Witt, Germany), color using Minolta colorimeter (Konica Minolta, Ramsey, NJ), texture using TA-XT2 texture analyzer (Texture Technologies Corp, Scarsdale, NY), and total soluble solids (Brix) using optical refractometer (Fisher Scientific, Bridgewater, NJ).
During the shelf-life study, the performance of PSA will also be evaluated. At the same time when examining the product, PSA’s whitening and initial adhesion strength will be evaluated using previously mentioned methods to investigate the effect of product type, temperature, and storage time, and subsequent adhesion strength will be evaluated after the first evaluation. The wait time between the two evaluations will range from 24 h to a time when the product expires, and during the wait time, samples will be stored back in the environment they are previously assigned to control the temperature and product’s respiration rate.
To the date of submitting the annual progress report, we were able to achieve one objective of the research, which is to optimize the performance of the peel-reseal lidding films. We were able to select two PSAs as candidates with good adhesion properties and strong resistances against whitening for different future peel-reseal packaging applications.
Initially, all 20 PSA candidates were coated on untreated 1.5 mil PET films with 40-60 dyne/cm surface energy to test their resistance against whitening. For each PSA, the final dry coat weights were 3, 5, 10, and 20 g/m2. Only 5 PSAs passed the test, while 14 PSAs were plasticized and whitened at all coat weights, and 1 PSA was rejected due to an unpleasant strong odor. The remaining 5 PSAs with 4 different coat weights were later adhered onto heat-sealable corona-treated PET films to optimize the adhesion strength and coat weight. The results of the evaluations are summarized in Table 1.
Table 1. Comparison of peel strength and possible peel-reseal cycles of selected PSAs
Based on the resistance against whitening and adhesion properties, an acrylic-based PSA emulsion with 300–400 cps viscosity, and a styrene-butadiene rubber (SBR) based PSA emulsion with 550-600 cps viscosity were selected, and the final coat weight was determined at 10 g/m2 to minimize the susceptibility to whitening at high relative humidity (RH >90%). Their adhesion strength of 16 peeling-resealing cycles is shown in Fig. 8.
Fig. 8. Peel strength in 20 peel-reseal cycles of candidate PSA emulsions
To further improve the selected PSA’s resistance to whitening, PSAs were deionized with Amberlite IRN-150 ion exchange resin and stabilized to pH 9.0 with ammonium hydroxide solution. The principle of this practice was to reduce PSA’s affinity to water so that water cannot partially plasticize PSA to cause whitening, and an elevated pH can stabilize the PSA emulsion to achieve a uniform and stable water affinity. Fig. 9 shows that deionization of SBR emulsion improved the whitening resistance of the PSA. Lettuce was used in this test,and squash noodles will be tested to validate the results.
Fig. 9. Resistance against whitening of PSA emulsion and deionized PSA emulsion
Education & Outreach Activities and Participation Summary
The goal of the outreach plan is to share our project and results with farmers, product developers, and researchers to have a long-term impact on agricultural sustainability for squash farmers in NJ and wider agricultural communities.
The first step is to receive feedback from real customers. We will collaborate with HelloFresh to distribute freshly prepared samples to panelists and ask their feedback on squash noodles’ quality, packaging design, convenience, and their tendency to make a purchase, while providing all the necessary information including product shelf-life and the environmental friendliness of the packaging.
Based on customers’ feedback, we will improve our packaging and develop various products with HelloFresh. We will explore the possibilities of providing squash noodles in the same package with sauces/seasoning, such as pasta sauces and stir-fry seasoning. We will also explore the possibilities of providing squash noodles in the same package with other fruits, vegetables, and nuts, such as blueberries, carrots, cherry tomatoes, almonds, etc. Furthermore, we will explore the possibilities of providing squash noodles in family-size packages with divided trays containing different fruits and vegetables in different segments. Peel-reseal packaging can make such packages with divided trays more convenient as each segment can have specific OTR by adjusting the number and locations of microperforations, and each segment can be opened and resealed individually without affecting the gas components in other segments, as shown in Fig. 7.
Fig. 7. Illustration of a family-size package with peel-reseal lidding films sealed on divided trays
The next step is to share the results with squash farmers in New Jersey using connections from HelloFresh. We will ask for their feedback on technical challenges, processing designs, and concerns on costs. With their inputs, we will establish commercially viable processes for large-scale manufacturing of the packaging. Our goal is to allow farmers to benefit from squashes’ improved marketability at a cost-neutral position compared to the packaging they are currently using.
In the meantime, we will submit two publications to internationally recognized journals with our results to have impacts on future researchers and wider agricultural communities. We plan to submit one publication to Postharvest Biology and Technology (ISSN: 0925–5214) with our progress on the optimization of squash noodles processing, and we plan to submit one publication to Food Packaging and Shelf Life (ISSN: 2214–2894) with our work on the shelf-life extension of squash noodles using MAP with microperforated peel-reseal films. Future researchers can follow our steps to develop peel-reseal packaging based on bio-based biodegradable films and containers, and they can apply the technology and methods to other fresh produce to benefit the wider agricultural communities.
This project is aimed to add value to squashes grown in NJ to increase their marketability and utilization. By developing healthy squash-based meal solutions in functional recyclable packaging, we estimated that the final product can create economic benefits for NJ squash farmers and improve the sustainability of NJ squash farming.
In recent years, NJ squash farmers are facing steadily growing economic losses from squashes that are harvested but unsold. In 2020, 4,560,000 pounds of harvested squashes (16 % of total squash produced) were unsold, and the estimated value of these unsold squashes was over $2 million. Therefore, by reducing the amount of unsold squashes, NJ squash farmers can see significant economic benefits and subsequently improve the sustainability of their farming.
Our envisioned product is a ready-to-cook meal solution based on squash noodles, packed in convenient peel-reseal packaging with microperforated lidding films to modify the atmosphere inside the package and ensure product quality. This product has many features that customers nowadays are looking for, which are being healthy, nutritious, flavorful, fresh, and convenient, with superior quality and reduced environmental impact. As a result, this product will provide NJ farmers with an opportunity to rebrand NJ squashes and expand their markets to reduce the loss from unsold squashes and improve the sustainability of their farming.
Our research group sees sustainability as an important topic. We study food packaging, a topic associated with all three perspectives of sustainability. On one hand, food packaging has its own issues by having high environmental impact from raw material extraction and end-of-life treatment. On the other hand, food packaging is a possible tool to reduce food loss and food waste, which impairs agricultural sustainability by wasting agricultural resources and leading to economic losses for farmers. Therefore, one goal of our research group is to improve agricultural and food sustainability while not creating more environmental, economic, and social impacts from food packaging.
This project serves as the starting point for us to understand how food packaging can improve agricultural sustainability by improving the marketability of agricultural products and creating economic benefits for farmers. In this project, we used technologies such as flexible films, peel-reseal, and modified atmosphere packaging to improve the quality and convenience of an agricultural product. In the future, we will also apply other technologies such as controlled release packaging, antimicrobial packaging, ethylene scavenging, and intelligent packaging to further improve the quality, safety, shelf-life, traceability, and convenience of agricultural products to contribute to the bigger scope of agricultural sustainability.