Christine M. Nowakowski

Cloning of peptidase genes from Lactobacillus helveticus CNRZ 32

Lactic acid bacteria express a complex proteolytic enzyme system that is capable of hydrolyzing casein to amino acids. We have begun to examine the number and specificity of exopeptidases from Lactobacillus helveticus CNRZ 32. A genomic library of L. helveticus CNRZ 32 DNA fragments from a Sau3A partial digestion was constructed in Escherichia coli DH5α utilizing pJDC9. This library was screened for the presence of aminopeptidase, X-prolyl dipeptidyl aminopeptidase (X-PDAP), and dipeptidase activities by two methods. The first screening identified an aminopeptidase II (APII) and X-PDAP. The X-PDAP was determined to be present on four independent DNA inserts ranging in size from 3.5 to 7.7 kilobase pairs (kbp). EcoRI/EcoRV digests of these plasmids suggested that all inserts had 1.0 and 1.8 kbp fragments in common. The gene for APII was determined to be present on three independent DNA inserts ranging in size from 8.2 to 11.3 kbp. EcoRI digestion of these plasmids indicated that 1.2 and 1.8 kbp fragments were in common. The second screening identified an additional aminopeptidase (API), a di/tripeptidase (DTP) with prolinase activity, a broad-specificity dipeptidase (DPI), and a narrow-specificity dipeptidase (DPII). The insert size of clones expressing API, DTP, DPI, DPII were 4.8, 9.5, 5.8, and 6.3 kbp, respectively. Histochemical staining of native polyacrylamide gels from recombinant E. coli cultures demonstrated that the cloned peptidase co-migrated with native L. helveticus CNRZ 32 enzymes.

Mapping Moisture Sorption Through Carbohydrate Composite Glass with Fourier Transform Near-Infrared (FT-NIR) Hyperspectral Imaging.

Inherent changes in foods during storage are often caused by water sorption or desorption that often results in product matrix instability. Water sorption behavior differs depending on the matrix through which it moves. Often, concurrent phenomenon such as crystallization modifies water’s movement. We describe a novel use of hyperspectral imaging combined with Fourier Transform Near Infrared (FT-NIR) spectroscopy to map where water molecules are in two dimensions while concurrently quantifying the crystallization motif as water sorbs into a carbohydrate matrix over a month’s storage time. This methodology allows us to identify and quantify sucrose crystals formed within a carbohydrate matrix while also mapping water migration through this complex matrix. We compared corn syrup/sucrose blends where sucrose is supersaturated (high sucrose, HS), sucrose is below saturation (low sucrose, LS), sucrose below saturation with embedded sucrose crystals (LSS) and maltotriose is supersaturated within a corn syrup matrix (high maltotriose, LSM). This FT-NIR method was used to characterize water sorption through a carbohydrate matrix over time and measured both the propensity of the systems to form sucrose crystals and the influence sucrose crystals have on water sorption. We observed water diffusion was slower in lower sugar carbohydrate glasses, and the process of sorption was different. Amorphous systems supersaturated in sucrose allow crystallization when sufficient water is sorbed and thus, this concurrent action disrupts normal Fickian diffusion. The water front compresses to a narrow band as it sorbs through the matrix. The presence of embedded crystals in an amorphous matrix slows overall water penetration through the matrix by convoluting the path of moving water molecules. This did not appear to change the rate of diffusion. Experiments with maltotriose at supersaturation concentration showed the crystallization rate was slower than sucrose. Thus, pure maltotriose is not a practical solution as a potential replacement for sucrose to slow sorption in food systems.

Non-equilibrium States in Confectionery

Many confections are governed by non-equilibrium states and glass transitions, both during manufacture and throughout shelf life. In general, sugar confections contain sucrose and glucose syrup as the main sweeteners, along with a variety of additives that distinguish each class of confections. The sugar syrup is boiled to remove excess water, and the final cook temperature determines the final water content through the boiling point elevation curve. During cooling, other ingredients may be added (e.g., colors, flavors, and acids) and/or other operations performed (e.g., aeration), again to distinguish the class of confections. Upon cooling to ambient temperatures, these confections generally are categorized as supersaturated solutions, in either the amorphous or glassy state. As such, they are unstable and prone to changes during storage, which may include moisture uptake or loss, crystallization, and flavor loss. This chapter will provide an overview of manufacture and formation of these products before delving into stability during storage and the mechanisms of collapse.

Making Your Way in a Company

You’ve worked hard in school and now you find yourself starting your career in industry. The beautiful thing about food science is that you can come from a variety of disciplines with one common thread, an interest in food. Unfortunately, that is precisely the challenge I have trying to describe a typical job in the food industry to you. Food science is a catch-all for engineering, biotechnology, chemistry, material science, microbiology, and law among other things. This diversity allows food scientists to fit in a company in a variety of positions within quality and regulatory and research and development (R&D). No matter where you work, government or industry, large or small company, you will require interpersonal skills and technical excellence in order to succeed. In general, the demands of a full-time job require skills that are not taught in college and how well you handle the demands of the job strongly influence one’s personal sense of accomplishment and life balance. It is critical to build in external input to maintain perspective and clearly see the next steps in your career. Here are some things to consider as you start out in your career.