Razvoj metod na NIR spektrometru za ovrednotenje kakovosti kakava in kakavovega masla

Podobnik, Pia (avtor), Kralj Cigić, Irena (mentor), Brodnik, Helena (komentor)

Analizne metode, ki se uporabljajo za nadzor kakovosti in pristnosti kakavovih surovin ter njihovih derivatov v industriji in raziskovalnih laboratorijih, so bile doslej večinoma konvencionalne. Zanje so značilni koraki, kot so vzorčenje, priprava vzorcev za ekstrakcijo ciljnih spojin in kvantitativno določanje vsebnosti analita z uporabo kemijskih reagentov. Večina teh metod je standardiziranih in se uporabljajo zlasti za spremljanje in optimizacijo procesa proizvodnje. Industrija pa ima vedno večjo potrebo po hitrih in nedestruktivnih metodah. Najbolj pogosta je spektrometrija, ki se izvaja v bližnjem kot tudi srednjem infrardečem območju in se večinoma uporablja za analizo biokemijskih parametrov kot so vsebnost celokupnih maščob, polifenolov, metilksantinov, itd. Cilj magistrskega dela je bil razviti nove metode na NIR (ang. near infrared) spektrometru za hitro ovrednotenje kakovosti kakavove mase in kakavovega masla. Analizirala sem 40 vzorcev kakavove mase in 40 vzorcev kakavovega masla, od katerih sem 30 vzorcev uporabila za postavitev kalibracijskih modelov in 10 za validacijo novopostavljenih NIR umeritvenih premic. Kakavovi masi sem z uporabo uradnih metod določila vsebnosti celokupne maščobe in teobromina, kakavovemu maslu pa vsebnost celokupnih prostih maščobnih kislin izraženih kot oleinska kislina in vrednost jodovega števila. Vsebnost celokupne maščobe sem določila z ekstrakcijo s pomočjo Soxletove destilacije. Teobromin sem določila z ekstrakcijo analita v vodo in ekstrakt analizirala s HPLC (tekočinska kromatografija visoke ločljivosti, ang. high performance liquid chromatography) z UV detekcijo. Vsebnost celokupnih prostih maščobnih kislin izraženih kot oleinska kislina sem določila z nevtralizacijo kislin s titracijo s kalijevim hidroksidom, jodovo število pa z uporabo Wijs metode. Za preverbo pravilno določenih vrednosti, sem rezultate istih parametrov istih vzorcev primerjala z rezultati pridobljenimi v zunanjem akreditiranem laboratoriju. Za razvoj metod sem posnela NIR spektre in na podlagi rezultatov, pridobljenih z uradnimi metodami, postavila umeritvene premice ter tako razvila indirektne metode. Umeritvene premice sem postavila z uporabo programa PerCal® Plus, kjer sem postavila različne modele s testiranjem regresij PLS in HR ter predobdelav harmonizacija in Savitzky-Golay filter v kombinaciji z detrendizacijo in SNV. Modele sem med seboj primerjala glede na vrednost modela, korelacijo, R$^2$, RMSE, SECV, Q$^2$ in R$^2$ validacije.

• Jezik: Slovenski jezik
• Ključne besede: kakavova masa, kakavovo maslo, NIR, umeritvene premice
• Vrsta gradiva: Magistrsko delo/naloga
• Tipologija: 2.09 - Magistrsko delo
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2025
• PID: 20.500.12556/RUL-171437
• COBISS.SI-ID: 247613699
• Datum objave v RUL: 26.08.2025

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Development of methods on the NIR spectrometer for evaluating the quality of cocoa and cocoa butter

Izvleček

Analysis methods used for quality and authenticity control of any raw materials and their derivatives in industry and research laboratories have been mostly conventional so far. They are characterized by steps such as sampling, sample preparation for extraction of target compounds and quantitative determination of analyte content using chemical reagents. Most methods are standardized and are used mainly for monitoring and optimizing the production process. However, the industry has an increasing need for fast and non-destructive methods. The most common is spectrometry, which is performed in the near and mid-infrared range and is mainly used for the analysis of biochemical parameters such as the content of total fats, polyphenols, methylxanthines, etc. The aim of the master's thesis was to develop new methods on a NIR (near infrared) spectrometer for rapid evaluation of the quality of cocoa mass and cocoa butter. 40 samples of cocoa mass and 40 samples of cocoa butter were analysed, of which 30 samples were used to build calibration models and 10 samples were used for validation of newly established NIR calibration lines. The total fat and theobromine content of cocoa mass, and the total free fatty acid content, expressed as oleic acid, and the iodine value of cocoa butter were determined using classical methods. The total fat content was determined by extraction using Soxhlet distillation. Theobromine was determined by extraction of the analyte into water and the extract was analysed by HPLC (high performance liquid chromatography) with UV detection. The content of total free fatty acids, expressed as oleic acid, was determined by neutralization of acids by titration with potassium hydroxide, and the iodine value was determined using the Wijs method. To verify the correctly determined values, the results of the same parameters of the same samples were compared to the results obtained in an external accredited laboratory. For method development, NIR spectra were recorded and calibration lines were established based on the results obtained with classical methods, thus indirect methods were developed. The calibration lines were fitted using PerCal® Plus, where different models were fitted by testing PLS and HR regressions and pretreatments harmonization and the Savitzky-Golay filter in combination with detrendization and SNV. The models were compared based on model value, correlation, R$^2$, RMSE, SECV, Q$^2$ and R$^2$ of validation.

• Ključne besede: cocoa mass, cocoa butter, NIR, calibration lines