Pomen določanja hrapavosti, zeta potenciala in mejnega kota površine sadja

Gorenc, Marija (avtor), Vidrih, Rajko (mentor)

Skozi celotno obdobje rasti se mora koža sadja nenehno prilagajati povečanemu volumnu ploda in ima pomembno zaščitno funkcijo. Kožica je sestavljena iz primarne kože, povrhnjice in kožice oz. kutikule. Kutikula je zgornja hidrofobna plast, ki sadežu daje mehansko podporo in sadje varuje pred insekti, izgubo vode in ultravijoličnim sevanjem. Glavni cilj diplomske naloge je bil preučiti hrapavost, zeta potecial in mejni kot površine sadja. Pomembno vlogo imajo tudi kutikularni voski, ki ščitijo plod pred fizikalnimi (npr. sprememba temperatura, sevanje UV), kemičnimi (npr. fitofarmacevtska sredstva) in biološkimi spremembami (npr. mehanske poškodbe, insekti). Bakterije se na površino sadja lahko pritrdijo z adhezini, bički, fibrijami in zunajceličnimi polisaharidi. Pri pritrdljivosti bakterij pa imata pomembno vlogo hidrofobna celična površina in površinski naboj bakterij. Lastnosti površine sadja lahko določimo z mejnim kotom, zeta potencialom, mikroskopijo na atomsko silo ali vrstično elektronsko mikroskopijo. Pri mejnem kotu merimo kot, ki nastane med molekulami v kapljici in trdno površino pod njo. Pri tem velja, da večji kot je mejni kot, večja je hidrofobnost površine. Vsebnost voskov in trihomov na površini sadja je v povezavi z mejnim kotom, saj je zaradi hidrofobne narave le-teh mejni kot večji. Zeta potencial prikazuje površinski naboj delcev, odbojne koloidne sile med njimi in fizično stabilnost sistemov, pri čemer velja, da je koloidni sistem bolj stabilen pri večjem zeta potencialu. Za mikroskopijo na atomsko silo je značilna velika povečava z veliko ločljivostjo, kjer lahko pridobimo tudi slike 2D in 3D. Pri vrstični elektronski mikroskopiji gre za pridobivanje informacij s pomočjo vedenja elektronov in za ustvarjanje tridimenzionalnih slik o mikrostrukturi površine sadja. S pomočjo mikroskopije na atomsko silo in vrstične elektronske mikroskopije smo ugotovili, da se hrapavost sadja razlikuje glede na sorto in stadij zrelosti. Z vrstično elektronsko mikroskopijo smo ugotovili, da se bakterije redko pritrjujejo na gladko površino sadja in da jih pogosto najdemo v mikrorazpokah.

• Jezik: Slovenski jezik
• Ključne besede: sadje, površina sadja, kutikula, poobiralne spremembe, mejni kot, zeta potencial, mikroskopija, pritrditev bakterij
• Vrsta gradiva: Diplomsko delo/naloga
• Tipologija: 2.11 - Diplomsko delo
• Organizacija: BF - Biotehniška fakulteta
• Kraj izida: Ljubljana
• Založnik: [M. Gorenc]
• Leto izida: 2022
• PID: 20.500.12556/RUL-137469
• UDK: 634.1/.7:664.8
• COBISS.SI-ID: 112329987
• Datum objave v RUL: 18.06.2022

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: The importance of determination the roughness, zeta potential and contact angle of fruit surface

Izvleček

Throughout the growing period, the fruit skin must constantly adapt to the increased volume of the fruit and it must maintain an important protective function. The cuticle consists of the primary skin, the epidermis and the dermis or cuticle. The cuticle is the top hydrophobic layer that provides mechanical support to the fruit and protects it from insects, water loss, and UV radiation. The main goal of this diploma thesis was to study the roughness, zeta potential and contact angle of the fruit surface. Cuticular waxes also play an important role in protecting the fruit from physical (temperature changes, UV radiation), chemical (pesticides), and biological changes (mechanical damage, insects). Bacteria can attach to the fruit surface through adhesins, flagella, fibrils and exopolysaccharides. However, the hydrophobic cell surface and the surface charge of bacteria play an important role in bacterial adhesiveness. Fruit surface properties can be determined by contact angle, zeta potential, atomic force microscopy, or scanning electron microscopy. The contact angle measures the angle formed between the molecules in the droplet and the solid surface beneath it. The higher the contact angle, the greater the hydrophobicity of the surface. The content of waxes and trichomes on the surface of the fruit is related to the contact angle, because of their hydrophobic nature, therefore contact angle is higher. Zeta potential shows the surface charge of the particles, the repulsive colloidal forces between them and the physical stability of the systems, with colloidal systems being more stable at higher zeta potentials. Atomic force microscopy (AFM) is characterized by high magnification with high resolution, where both 2D and 3D images can be obtained. Scanning electron microscopy (SEM) information is extracted from the behavior of electrons to produce three-dimensional images of the microstructure of the fruit surface. With microscopies AFM and SEM, we found that fruit roughness varies according to fruit species and stage of maturity. Using microscopy SEM, we also found that bacteria rarely attach to smooth fruit surface and are often found in microcracks.

• Ključne besede: fruits, fruit surface, cuticle, postharvest quality, contact angle, zeta potential, microscopy, bacterial adhesion