Using Fruit Spreads to Aid Research in the Undergraduate Laboratory

NINA BAGHAI-RIDING (nbaghai@deltastate.edu) is a professor, LARRY COLLINS (lcollins@deltastate.edu) is an instructor, and CHARLES SMITHHART (csmithrt@deltastate.edu) is an associate professor, all in the Division of Mathematics and Sciences at Delta State University, Cleveland, MS.

Course-based Research Experiences (CUREs) have been a growing area of interest for geoscience educators.Auchincloss et al., (2014) describes these courses as involving a whole class of students in the investigation of a research question that is also applicable to a larger scientific community. CUREs must enable students to make discoveries by collecting and analyzing data to get results that are informative to the broader scientific community (Spell et al., 2014). At Delta State University, upper-division undergraduate science laboratories are transformed into an experience where students engage in collaboration, conduct authentic research, and have practice in communicating scientific findings. Two courses, Methods and Materials of Environmental Science (BIO 415) and Instrumental Analysis (CHE 460), provide opportunities for students to compare elements found in fruit spreads (jams/jellies/marmalades/preserves) from different areas of the United States (Figure 1) to soils in which the fruits were grown. Students prepared the samples for analysis using the JSM-6010LA SEM (Scanning Electron Microscope) with EDS (Energy Dispersive X-Ray Fluorescence Spectroscopy) attachment to identify the elemental composition of each sample's ash. The learning objectives were to determine the chemical composition of the fruit spread ashes and grasp how soil chemistry influences chemical uptake in plants, interpret data by compiling tables, graphs, and images, incorporate data from Natural Resources Conservation Service (NRCS) soil website into their data analysis, and gain proficiency with the scientific method. Procedures and results for both courses are highlighted along with key results which emerged from the project over the last few years (2017-2021).

Methods and Materials

During the spring semesters (2017-2021), BIO 415 students would select from a variety of hands-on, semester long projects; class sizes ranged from 10–15 students per semester. Students enjoyed the fruit spread project over other projects done in past semesters. Materials needed included electronic analytical balances that measured to 0.0001 gram, a hot plate (Figure 2A), evaporating dishes, porcelain crucibles with lids that can withstand temperature over 1100˚ C, metal spatulas, a metal rack for holding the crucibles in place (Figure 2C), a front-loading benchtop muffle furnace for ashing samples over 1000˚ C (Figure 2D), scintillation vials with screw-top lids (Figure 2F), a scanning electron microscope which has x-ray fluorescence capabilities for elemental analysis, Munsell color charts, and computers with Internet access. Most of the chemistry supplies are associated with quantitative analysis or inorganic chemistry labs. 

Fruit spreads were acquired from colleagues of Dr. Nina Baghai-Riding or from local vendors that grew the fruit on their land and would turn it into a fruit spread. Most samples came from areas throughout the United States; one came from Great Britain. Students selected four to five fruit spreads they wanted to investigate during the semester. Throughout the semesters of this project, students preferred to study samples outside of the Mississippi Delta.

Each selected fruit spread was placed into an evaporating dish; the quantity of sample varied from 75–310 grams depending on the amount of material that was available. Fruit spreads were spaced a few inches apart on a hot plate and slowly heated for 7-14 days at 100˚ C to avoid sputtering and contamination with other samples (Figure 2A). Heating removed water and volatiles as well as consolidated, solidified, and dried out the samples; for best results, the fruit spread should be heated to the point of charring.

In the chemistry lab, students divided each condensed sample into five 20–50 mm crucibles using metal spatulas. Plastic spoons and spatulas could not be used because of the hardness of some of the condensed samples. Each crucible + lid's mass was measured to the nearest 0.0001 g on analytical balances before and after loading them with condensed sample to about two-thirds capacity. All masses were recorded on an Excel spreadsheet. The partial filling was done to avoid problems like stuck or displaced crucible lids due to further expansion of the condensed samples. The loaded crucibles with lids were then put in a grid-style steel rack and placed into a Fisher Isotemp Model 650-58 Muffle Furnace for 24 hours at 1,000˚ C to generate an ash. The crucibles were left several hours to return to room temperature and then reweighed. The ashes were then transferred to labeled 20 ml vials (Figures 2E-F).

The ash samples were later ground with mortar and pestles to reduce the ashes to homogenous powders. A magnet was used to remove any rust flake contamination that might have intruded from the sample rack during the ashing process. Conductive carbon discs with double-sided adhesive were attached to individual 10 mm aluminum SEM sample stubs. A small representative quantity of ash was fixed to the remaining exposed adhesive. No conductive coating was applied since the carbon discs provided the required conductivity. An aerosol duster, along with light tapping, was used to remove excess ash from the carbon discs to minimize SEM contamination. The stubs were placed into the scanning electron microscope chamber and measured with the integrated energy-dispersive x-ray (EDS) analyzer. The EDS analyzer is a common option ordered with SEMs to determine elemental composition (Figure 3). Students appreciated the ability to measure elements simultaneously and non-destructively. A ZAF-based matrix-correction algorithm calculated elemental abundances, which were assumed to be oxides. A table of percent composition and an XRF spectrum (Figure 3) were obtained for each fruit spread. SEM digital photographs also were taken of each sample to note textural differences. Munsell Soil Color Charts were used to determine the color of each ash. Local soil types for each sample were gathered from the NRCS soil website as well as from the homeowner/vendor who provided the fruit spread. The chemistry of the soil and surface strata were compared to the ash contents.

A small group of students enrolled in BIO 415 created a scientific poster of the various fruit spread samples that were analyzed each spring semester. All the students were expected to be competent in using a Munsell Soil Color Chart and the NRCS website and using analytical balances. Students who were also enrolled in Instrumental Analysis learned about EDS and prepared specimen stubs for analysis on the SEM. These students were expected to explain the physics of X-ray production associated with an SEM and to understand the limitations and advantages of EDS analysis as compared to other spectroscopic elemental analysis methods. Test questions were given on the summative exam and students also produced XRF (X-Ray Fluorescence) spectra for lab reports. Although these results were not collated year to year, Instrumental Analysis students were able to report their findings into an acceptable scientific format that met requirements for the American Chemical Society. 

Students gained experience collaborating with each other and the instructors. Collaborating skills were demonstrated when mentoring their peers on sample preparation as well as developing and constructing scientific posters that were reviewed by other class participants. Posters were designed using Adobe Illustrator or Photoshop. Two class posters were given at the Mississippi Academy of Sciences (Masterson et al., 2018; Bellamy, 2020) and at the Botanical Society of America (Masterson et al., 2017). A presentation and a short paper was presented at the Perm University/Delta State University biology teleconference (Bellamy, 2018). These presentations received good reviews by conference attendees.

To conduct a similar study, instructors could use a hand-held EDXRF to conduct the elemental analyses rather than a SEM with EDS. To eliminate water, evaporating dishes containing the fruit spread could be placed in a microwave until the sample starts to char if time is a factor. Instructors who want to adopt this approach as a laboratory instruction need to be aware that students will need to be mentored as they conduct each procedure. Most can do the steps without supervision after performing the procedure once. Modeling how scientists think, make sense of data, and report on data will also help students gain a stronger understanding of the nature of science.

Results

Weights of the ash samples ranged from 0.00 g to 0.3766 g. The blue elderberry jelly from Nevada generated the most ash; the peach jam from Virginia possessed no ash (its weight was from rust flakes from the crucible rack). Most ash colors were within the yellow to yellow-red hue range of the Munsell Color Chart. The natural strawberry sample from Dripping Springs, TX, possessed a green-yellow hue.

Each ash sample possessed a unique texture and appearance when viewed using the JEOL scanning electron microscope. For example, the Vicksburg, MS, muscadine jam ash resembles thin flat sheets; the Tucson, AZ, cactus marmalade ash compacts into fine irregular masses; and the East Lyme, CT, blueberry ash forms irregular waves (Figure 4.)

A total of 22 elements were noted from the 27 ash samples. The elemental content of each sample was unique (Table 1). The number of elements ranged from 6 to 13 (mean = 9.4). Elements contained in every sample included carbon and oxygen. Common elements (³ 20 occurrences) included magnesium, phosphorus, silica, and calcium and elements with frequent occurrences (15 – 19 occurrences) included sodium and potassium. Several elements found in fewer than two samples included arsenic, nickel, vanadium, zirconium, and molybdenum.

Similar fruit spreads from different areas of the USA possessed dissimilar elements. For example, the peach sample from Nampa, ID, possessed potassium, calcium, and manganese; the peach sample from Laurel, VA, contained aluminum and chromium; and the peach sample from Bear Lake, UT, had magnesium, calcium, and titanium. Additionally, the muscadine grape from Vicksburg, MS, possessed sodium and potassium; both elements were not contained in the muscadine grape sample from Cleveland, MS, (Figure 3A.) The blueberry rhubarb from Montague, MA, lacked the sulfur and silica which were found in the blueberry rhubarb sample from Maple Valley, WA.

In contrast, fruit spreads from the same location were variable in composition. For example, blackberry jam from Cleveland, MS, contained sodium, sulfur, and magnesium which were not found in the muscadine grape sample. Aluminum, titanium, molybdenum, and zirconium were found in the muscadine grape sample but were lacking in the blackberry sample from the same area. Different elemental groupings also occurred in other fruit spreads for the two samples acquired from East Lyme, CT, and Corrales, NM. For example, the low sugar strawberry sample from East Lyme, CT, possessed six elements whereas the blueberry jam possessed 10 elements; manganese, arsenic, sulfur, and aluminum were not present in the strawberry sample. The raspberry lavender jam sample from Corrales, NM, contained eight elements including magnesium, phosphorus, potassium, sulfur, calcium, and barium, whereas the raspberry red chili jam only contained four elements.

Through using resources such as the NRCS website, geological references that correlated to a local area, geologic maps, and personal communication with some participants who furnished the samples, it became apparent to students that soil composition varies throughout the United States. The variation in part may be reflective of disturbance events, geographical location, industrialization, age, runoff, and more. For example, nickel found in the Nampa, ID, peach sample may be from mineral tailings when this area was a gold mining town. Calcium spikes (peaks) associated with the jam/jellies from Lincoln County, NV, (Figure 3C), Montague, MA, and Bear Lake, ID, are reflective of limestone and/or calcium rich soils. Samples from Cleveland and Vardaman, MS, yielded the most elements, because they are from floodplain sediment. The raspberry lavender sample from Corrales, NM, possessed a large spike of magnesium which could reflect the presence of wind-blown dust or sedimentary deposits of high magnesium soil (Reheis et al., 2009) due to the raspberry farm being within proximity to the Rio Grande River. The raspberry habanero sample from Mariposa, CA, and blueberry rhubarb from Brookfield, MA, had high spikes of potassium and phosphorus, which may be from fertilizer applications to enhance soil suitability (Marles, 2016). The blueberry rhubarb from Maple Valley, WA, had a high sulfur spike that was not associated with the local geology but rather from sheep and poultry manure to aid in soil fertility (Marcia Knadle, written communication 2021).

Results from this study also indicate that plants are selective about what nutrients they need for growth and reproduction, but some plants may be more selective than others (Heidak et al., 2014). Root uptake is complex (Ould-Dada et al., 2003) and even small traces of soil elements may be found in edible fleshy fruits.

Conclusions

Overall, this project successfully provided students with the opportunity to conduct new research, collaborate with their peers, and discover new knowledge that is relevant to the broader scientific community. Occasionally, setbacks occurred throughout the semesters. For example, some fruit spreads required more than two weeks to process on the hot plate prior to putting them in the furnace, and crucible lids sometimes would slide off when the fruit spread was cooked down to an ash due to further volumetric expansion. As demonstrated in the results, students explored the chemistry of samples of fruit spreads across the US and correlated them with the soils in which the plants were grown. They became aware of how various geologic processes can influence the chemical composition of assorted fruit spread: river flooding, windblown loess, glacial deposits, volcanism, and more. They recognized that different fruits from the same region can possess an assemblage of dissimilar chemical elements and that the same type of fruit, such as peaches, may contain disparate accumulation of chemical elements from region to region (Table 1). Results from this study also can be used to demonstrate how human health/nutrition is tied to elements contained in soils. In some situations, some results were not related to the local lithology, but rather to human practices such as mining or adding nutrient-rich fertilizers like sheep manure which altered the original soil composition. Students were able to communicate these findings via posters, presentations, and published abstracts: Bellamy, Baghai-Riding, and Smithhart (2018, 2020); Masterson et al. (2017, 2018). Future work will continue to explore fruit spreads from other areas of the United States and abroad. This research may be extended to other local products throughout the United States such as salsa and maple syrup that would enhance and extend the CURE experience. Participation in this type of research project influences students' sense of place from a place-based education perspective.

Acknowledgments 

We are grateful to Mississippi IDeA Networks of Biomedical Research Excellence (INBRE) for funding a Scientific Education and Outreach grant and to Mississippi Space Grant Consortium (MSSGC)/NASA for providing financial support for this project. We would also like to thank Dr. Yongqin Zhang and Ebony Coles for their construction of the map. Lastly, feedback from Amber Hays and Redina Finch helped to improve the quality of this paper.

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